Raises masked AssertionError in _test_network_api

The _test_network_api method was catching an AssertionError to do some
more checking but failed to raise the original error if the checking
didn't hit any matches. This patch fixes the test to raise the original
assertion error.

Closes-Bug: #1212017

Change-Id: I33147d18e33cd4babfc3f5cb572007bc7e4c07e6
Merge "Raises masked AssertionError in _test_network_api"