Add unit tests covering single operations to ODL

This commit adds the remaining test cases (create and update
operations) to fully cover sync_single_resource. It also defines the
filter_* methods as static or class methods and removes their duplicate
arguments.

Conflicts:
        neutron/plugins/ml2/drivers/mechanism_odl.py

Closes-Bug: #1325184
Change-Id: I6b6153ea577bd685576690559b1c389490ee525d
(cherry picked from commit 903e2a8cd1dd9169048d1ad9dd8a566b2ae52395)
Merge "Add unit tests covering single operations to ODL" into stable/icehouse