Remove email as optional query parameter

Since in keystone it was decided that a user's email won't be taken as a
first class attribute, it is then needed to get it off the API as it is
not an attribute with which you can filter users.

Related-Bug: #1306835
Change-Id: I42957172ef4c90345cea14df45ce7f499dd20c89
Merge "Remove email as optional query parameter"