Avocado: Add 2 new loggers 'avocado.test.stdout' and 'avocado.test.stderr'

Both will be important to store stdout and stderr streams
of tests for our future output check mode feature.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.core.output: Add LogFile object

Add a new object that can properly stub the stdout
and stderr streams for test subprocess executions,
delivering the messages to our stdout and stderr
loggers instead of directly to sys.stdout and/or
sys.stderr.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.job: stub stdout and stderr of test subprocesses to loggers

So whatever goes to the stdout/stderr of those subprocesses
gets properly logged in the stdout.actual/stderr.actual files
that the test execution will record.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.test: Create the 'stdout.actual' and 'stderr.actual' files for tests

Create the file handler for both streams and connect them to
the loggers, so whatever goes on the stdout of those tests
will be logged to those files.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.utils.process: Add record_stream_files param to APIs

Add the new record_stream_files to the process APIs, which
basically means, 'log stdout and stderr of that subprocess
to the test stdout.actual and stderr.actual files'. We
thought about making that transparent, but frequently people
will want to execute programs inside tests that are part
of the setup of those tests, for example, make commands and
the such.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
examples/tests/synctest.py: Add record_stream_files arg to synctest call

Add the record_stream_files argument to the synctest
command execution, to showcase how to use it. The idea
is that the full output of the synctest command goes to
the 'stdout.actual' and 'stderr.actual' files, excluding
all previous 'make' commands used to build the test suite.

With this, we pave the way for a feature that people can
use to record the outputs of commands, and later compare
with the reference output automatically.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>