Use keystonemiddleware and manila.conf for config

Switch to keystonemiddleware so a full keystoneclient installation is no
longer required.
Also move the configuration parameters for auth_token from api-paste.ini
to manila.conf. api-paste.ini configuration can still be used and take
priority over parameters from manila.conf.
Finally adjust devstack lib and use manila.conf to configure auth_token.

Related-Bug: #1240753
Change-Id: I4317ffca174a0f73dddc7030b367d49130040c77
Merge "Use keystonemiddleware and manila.conf for config"