object-storage: Initial unittest of DiskFile class

If we had this ahead of time, we could have avoided the errors that
were encountered leading to the fix-account-mapping fix (see
http://review.gluster.org/4222).

This represents 100% coverage of the DiskFile module, but the coverage
report says otherwise, unfortunately. That is because the put() method
invokes eventlets during the test run, and coverage is not able to
accurately track the coverage lines properly. If one comments out the
"tpool.execute()" line in DiskFile.put() the coverage report is then
100%.

Additionally, we changed DiskFile.put() in four ways that should not
change its behavior:

  1. Comments were added to explain various code paths and mark
     potential issues / fixes

  2. It no longer returns a boolean value, matching the behavior of
     swift.obj.server.DiskFile.put()

  3. It no longer logs a message when it detects a directory that
     already exists, instead is raises an exception

     We believe this is okay because we cannot find a code path that
     would lead to his condition. As a result, it makes it easier to
     test all the code paths in that routine.

  4. It no longer logs a message when create_dir_object() fails, since
     create_dir_object() raises an exception on failure only

     We also modified create_dir_object() to not return a boolean as a
     result of the above behavior.

Note that by implementing these tests up to this point we found three
code paths that would have failed if encountered due to missing
imports. We also made changes to the DiskFile module to make it a bit
easier to test, also eliminating an extra stat system call when
deleting directory objects.

Change-Id: I3286de83c1ec7c5e8d6cab9354e1c4397cee7497
BUG: 870589
Signed-off-by: Peter Portante <peter.portante@redhat.com>
object-storage: a set of cleanups to DiskFile

Here are a set of cleanups for things noticed while working on the
unit test coverage:

  * Remove unused constants, adding a constant for default disk chunk
    size

  * Document missing logger parameter from constructor

  * Add iter_hook paramater to constructor in anticipation of 1.7.4
    support

  * Add back meta_file field even though it is not used in our version
    of the constructor for paranoid compatibility

  * Remove is_valid field as it is not referenced anywhere, and it is
    not a field of the super class

  * Rename fields only used internally by DiskFile with leading
    underscores

  * Convert to using os.path.join() instead of hard coded '/'
    references

  * Use data_file field where possible

  * Assert that put_metadata() will only work when the file exists

  * Remove update_object() method since it is identical to
    put_metadata() and a direct write will suffice

  * Create the directory object only if it does not exist when a
    marker directory is requested

Change-Id: If207fed4c0f423e6bd3232e4507f87de877057c4
BUG: 876660
Signed-off-by: Peter Portante <peter.portante@redhat.com>
object-storage: apply upstream DiskFile refactor

Apply the upstream DiskFile refactoring in ahead of its use to easiliy apply
the temp file optimization.

Change-Id: I2708733eed3d87759c70eb3d9e6cd74ef91d0c7b
BUG: 876660
Signed-off-by: Peter Portante <peter.portante@redhat.com>
object-storage: do not list directory for delete

Do not list the entire directory contents of the directory containing the file
before deleting it. We have already verified the files existence constructing
the Gluster_DiskFile object.

This fixes a customer issue. See 885281
(https://bugzilla.redhat.com/show_bug.cgi?id=885281).

Change-Id: I4425c42af3e03624370c779d74b7f073e6eef024
Signed-off-by: Peter Portante <peter.portante@redhat.com>