add the user/pass to the keystone_settings hash

The intention is to move the code duplicated in each
cookbook (e.g. cinder, ceilometer, nova) from COOKBOOKHelper into this
central KeystoneHelper where it can be used by all of them.
refactor chef search and result processing
Merge pull request #213 from mapleoin/keystone-settings

add the user/pass to the keystone_settings hash
Fix trust backend setting

Don't set the token driver as trust backend, it does
not work at all.
Merge pull request #223 from dirkmueller/release/stoney/master

Fix trust backend setting