Consoldidate wifi test suite boilerplate into site_wifitest.py

Every time we create a wifi test suite, we have to copy the
boilerplate code from a previous suite.  In the spirit of DRY,
I've consolidated things into a superclass for the .py code
and a site_wifitest call for the control file.

BUG=none
TEST=rerun run_remote_tests

Review URL: http://codereview.chromium.org/3431008
5 files changed