project membership to role conversion

Changes the relationship between users and projects.
There is no more direct membership in projects.  Instead,
all membership is now done via roles.
A default role has been created called _member_ with a uuid (both
configurable) that will be added in place of the group membership
for databse upgrades.

DocImpact:  https://bugs.launchpad.net/openstack-manuals/+bug/1087483

Change-Id: I2482f9ef7b838e5dade5096d6d00e81db71604d1
Merge "project membership to role conversion"