Revert "Default to keystone auth strategy"

There seem to be some issues with this in instack. The 
investigation is ongoing and this change will be reinstated once 
the problem is resolved.

This reverts commit 1adfb6ccd46471bba14b007b3364bb1d8a5ffd04.

Change-Id: I65502784bfc5d874f4bf3b74f1370fb9f8bb54bd