Allow test_l3_agent unit test to run individually

When the test_l3_agent.TestL3AgentEventHandler test case is run
after test discovery it passes because discovery imports files
that registers all the config options. For the test case to run
individually we need to explicitly register the config options
used in the test.

Change-Id: Ic31503ad7be8601ff843dbdc8edf5856ce8b0e39
Closes-bug: #1313812
Big Switch: Check source_address attribute exists

Check that the source_address attribute exists on
HTTPSConnection objects before referencing it since
it's not present on python 2.6 deployments.

Closes-Bug: #1316382
Change-Id: Id82e70f124cba73c33737099027b5c61aea713bb
Disable debug messages when running unit tests

Some runs started to fail due to large sub_unit.log files. We should
reduce their size. The easy way to achieve this is to disable INFO
messages that are filling our logs.

Change-Id: I6b3d3a4498593b6b5635d7eded4f9f88c84e5da0
Closes-Bug: 1316610
Merge "Big Switch: Check source_address attribute exists"
Merge "Disable debug messages when running unit tests"
Merge "Allow test_l3_agent unit test to run individually"