Do not assume order of parameters in OVSBridge.add_flow call

Do not assume order of parameters in OVSBridge.add_flow call

This fixes neutron.tests.unit.agent.linux.test_ovs_lib.OVS_Lib_Test.test_add_flow
unit test that breaks with a randomized PYTHONHASHSEED.

The test assumed that the parameters passed to add_flow had
elements in a particular order. Found with PYTHONHASHSEED=2455351445.
The fix refactors the test case to match parameters as set.

Partial-bug: #1348818

Note: There are several other unrelated unit tests that also break with a
randomized PYTHONHASHSEED, but they are not addressed here. They will be
addressed in separate patches.

Change-Id: Ibe2f4d929b8b42c8c909c2306d2554faf7109b49