object-storage: Import missing sys and errno modules.

Import the missing modules and implemented unit test case for Glusterfs module.
Thanks to Paul Smith for pointing it out.

Change-Id: Ib04202aa0ae05c4da2ebbf11f87d6accc778f827
BUG: 905946
Signed-off-by: Mohammed Junaid <junaid@redhat.com>
Reviewed-on: http://review.gluster.org/4758
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>