tests: Use more clear name

false_mock is misterious name, specially when used as false_mock=False.
Reading the code reveal that false_mock=True means that the mock should
fail. Hopefully renming it to should_fail will make this more clear.

When creating a mock, using optional argument notation "should_fail=True"
is more clear then just "True".

Change-Id: I0697923fb18eb0d7d35e8044da7f6b4f8ee9d051
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/32726
Reviewed-by: mooli tayer <mtayer@redhat.com>
Reviewed-by: Allon Mureinik <amureini@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>