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. If it
does not exist, create a socket connection without
specifying the source.

Closes-Bug: #1316382

Conflicts:

	neutron/tests/unit/bigswitch/test_servermanager.py

Change-Id: Ica10d23cc6de81ae56f711937f208c7321c77f36
(cherry picked from commit f5e4cf8e3edd1ce0ebb8c0c7256be07d094896de)