BigSwitch: Stop HTTP patch before overriding

Stops the default HTTPConnection patch used by the
Big Switch tests before patching HTTPConnection with
another substitution. This prevents mock from losing
track of the default patch which was resulting in it
not consistently being stopped by the stopall call in
cleanup.

This also corrects an incorrectly targeted mock for the
HTTP patch in one of the test files.

Closes-Bug: #1303605
Change-Id: Ia5b374c5f8d3a7905d915de4f1f8d4f3a6f0e58d
Merge "BigSwitch: Stop HTTP patch before overriding"