Added url_path_replace and has_in_url_path methods

utils.py, views.py and backend.py were using .replace('v3', 'v2.0') and
.replace('v2.0', 'v3') methods on url strings.
This is BAD because if you have v3 in your url's domain it brakes it.

A new url_path_replace method now only performs the replaces in the url path
and leaves the domain unchanged.

Some checks where performed to test if a substring was in the url path but the
tests where performed on the whole url and could return a false positive if the
substring exists in the domain name or in the query string.
The new has_in_url_path method checks only if the substring is in the path of
the url.

Change-Id: I030d928d83e5c91cf26101221649a299d146747d
Closes-Bug: 1324948
Merge "Added url_path_replace and has_in_url_path methods"