qemu-iotests: allow passing unittest.main arguments to the test scripts

qemu-iotests: allow passing unittest.main arguments to the test scripts

Python test scripts that use unittest consist of multiple tests.
unittest.main allows selecting which tests to run, but currently this
is not possible because the iotests wrapper ignores sys.argv.

unittest.main command line options also allow the user to pick the
desired options for verbosity, failfast mode, etc.  While "-d" is
currently translated to "-v", it also enables extra debug output,
and other options are not available at all.

These command line options only work if the unittest.main testRunner
argument is a type, rather than a TestRunner instance.  Therefore, pass
the class name and "verbosity" argument to unittest.main, and adjust for
the different default warnings between TextTestRunner and unittest.main.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Tested-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20210323181928.311862-3-pbonzini@redhat.com>
Message-Id: <20210503110110.476887-3-pbonzini@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>