bin/bitbake: Ensure early errors are shown to the user

Currently if errors occur early in the init process, the errors may
not be shown to the user. This change ensures that if a failure does
occur, the messages are flushed from the queue and shown to the user.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
utils: Improve better_exec traceback handling

The current bitbake tracebacks are hard to read/confusing and sometimes
incomplete. This patch attempts to do better by:

* Moving the note about the exact exception to the end to make things
  read in sequence
* Merged the initial stack trace to become part of the code dump
* Added handling for "/xxxx" file paths since we can load these files
  and include the data as part of the trace
* Dropped the ERROR: prefix to every line, allowing the error messages to
  be spacially accosicated in the UIs
* Moved the "From:" line to the top of each code block and ensured its present
  consistently

With the complexity now in this funciton, I've added try/except wrapping around
it to ensure we catch exceptions in the exception handler too.

Example before:

"""
ERROR: Error executing a python function in /media/build1/poky/meta/recipes-core/eglibc/eglibc-initial_2.17.bb:
TypeError: 'filter' object is not subscriptable

ERROR: The stack trace of python calls that resulted in this exception/failure was:
ERROR:   File "do_populate_lic", line 13, in <module>
ERROR:
ERROR:   File "do_populate_lic", line 6, in do_populate_lic
ERROR:
ERROR:   File "license.bbclass", line 99, in find_license_files
ERROR:
ERROR:   File "/media/build1/poky/meta/lib/oe/license.py", line 38, in visit_string
ERROR:     if pos > 0 and license_pattern.match(elements[pos-1]):
ERROR:
ERROR: The code that was being executed was:
ERROR:      0009:    destdir = os.path.join(d.getVar('LICSSTATEDIR', True), d.getVar('PN', True))
ERROR:      0010:    copy_license_files(lic_files_paths, destdir)
ERROR:      0011:
ERROR:      0012:
ERROR:  *** 0013:do_populate_lic(d)
ERROR:      0014:
ERROR: [From file: 'do_populate_lic', lineno: 13, function: <module>]
ERROR:      0002:def do_populate_lic(d):
ERROR:      0003:    """
ERROR:      0004:    Populate LICENSE_DIRECTORY with licenses.
ERROR:      0005:    """
ERROR:  *** 0006:    lic_files_paths = find_license_files(d)
ERROR:      0007:
ERROR:      0008:    # The base directory we wrangle licenses to
ERROR:      0009:    destdir = os.path.join(d.getVar('LICSSTATEDIR', True), d.getVar('PN', True))
ERROR:      0010:    copy_license_files(lic_files_paths, destdir)
ERROR: [From file: 'do_populate_lic', lineno: 6, function: do_populate_lic]
ERROR:      0095:        lic_files_paths.append((os.path.basename(path), srclicfile))
ERROR:      0096:
ERROR:      0097:    v = FindVisitor()
ERROR:      0098:    try:
ERROR:  *** 0099:        v.visit_string(license_types)
ERROR:      0100:    except oe.license.InvalidLicense as exc:
ERROR:      0101:        bb.fatal('%s: %s' % (d.getVar('PF', True), exc))
ERROR:      0102:    except SyntaxError:
ERROR:      0103:        bb.warn("%s: Failed to parse it's LICENSE field." % (d.getVar('PF', True)))
ERROR: [From file: 'license.bbclass', lineno: 99, function: find_license_files]
ERROR: Function failed: do_populate_lic
ERROR: Logfile of failure stored in: /media/build1/poky/build/tmp/work/i586-poky-linux/eglibc-initial/2.17-r3/temp/log.do_populate_lic.17442
"""

Example after:

"""
ERROR: Error executing a python function in /media/build1/poky/meta/recipes-core/eglibc/eglibc-initial_2.17.bb:

The stack trace of python calls that resulted in this exception/failure was:
File: 'do_populate_lic', lineno: 13, function: <module>
     0009:    destdir = os.path.join(d.getVar('LICSSTATEDIR', True), d.getVar('PN', True))
     0010:    copy_license_files(lic_files_paths, destdir)
     0011:
     0012:
 *** 0013:do_populate_lic(d)
     0014:
File: 'do_populate_lic', lineno: 6, function: do_populate_lic
     0002:def do_populate_lic(d):
     0003:    """
     0004:    Populate LICENSE_DIRECTORY with licenses.
     0005:    """
 *** 0006:    lic_files_paths = find_license_files(d)
     0007:
     0008:    # The base directory we wrangle licenses to
     0009:    destdir = os.path.join(d.getVar('LICSSTATEDIR', True), d.getVar('PN', True))
     0010:    copy_license_files(lic_files_paths, destdir)
File: 'license.bbclass', lineno: 99, function: find_license_files
     0095:        lic_files_paths.append((os.path.basename(path), srclicfile))
     0096:
     0097:    v = FindVisitor()
     0098:    try:
 *** 0099:        v.visit_string(license_types)
     0100:    except oe.license.InvalidLicense as exc:
     0101:        bb.fatal('%s: %s' % (d.getVar('PF', True), exc))
     0102:    except SyntaxError:
     0103:        bb.warn("%s: Failed to parse it's LICENSE field." % (d.getVar('PF', True)))
File: '/media/build1/poky/meta/lib/oe/license.py', lineno: 38, function: visit_string
     0034:        new_elements = []
     0035:        elements = filter(lambda x: x.strip(), license_operator.split(licensestr))
     0036:        for pos, element in enumerate(elements):
     0037:            if license_pattern.match(element):
 *** 0038:                if pos > 0 and license_pattern.match(elements[pos-1]):
     0039:                    new_elements.append('&')
     0040:                element = '"' + element + '"'
     0041:            elif not license_operator.match(element):
     0042:                raise InvalidLicense(element)
Exception: TypeError: 'filter' object is not subscriptable

ERROR: Function failed: do_populate_lic
ERROR: Logfile of failure stored in: /media/build1/poky/build/tmp/work/i586-poky-linux/eglibc-initial/2.17-r3/temp/log.do_populate_lic.3275
ERROR: Task 9 (/media/build1/poky/meta/recipes-core/eglibc/eglibc-initial_2.17.bb, do_populate_lic) failed with exit code '1
"""

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
utils: Improve better_compile error message

Similarly to the better_exec improvements, improve the compile failure
messages to be more user readable.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bin/bitbake: add a check for /dev/shm existing

Python multiprocessing needs /dev/shm, and if it doesn't exist (e.g. in
a chroot environment) or is not writable, you'll get
"OSError: [Errno 38] Function not implemented" or
"OSError: [Errno 13] Permission denied" with a traceback, which doesn't
really help to explain what is wrong.

Implements [YOCTO #4407].

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>