PYCBC-544: Handle regex assert compatibility properly
PYCBC-544: Handle regex assert compatibility properly

Implement AssertRaisesRegex for Python 2.7 and only try
AssertRegexpMatches if the method is missing rather than
if the original call fails, otherwise
we will get a confusing error message on Python 3
when the assertion fails.

Change-Id: I2f1b86f6ec22be33f7b9d3b4df6f0275af311005
Reviewed-on: http://review.couchbase.org/101851
Reviewed-by: Mike Goldsmith <c43a3c67d7a1203c37ce25b098df0254011e1ce6@gmail.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

couchbase/couchbase-python-client,couchbase/couchbase-python-client