Build & deployment improvements

WIP for moving the haproxy cartridge's gear registry to the runtime
platform

Added oo-ssh to use for rsync/ssh as the gear user

Added "primary" endpoint option that indicates that the endpoint should
be load balanced if the app is scalable (along with
OPENSHIFT_LOAD_BALANCER_PORT)

Added microseconds to the deployment dir datetime to avoid collisions
in unit tests

:deployment_id is now optional for ApplicationContainer#distribute and
#activate. If not specified, they will use the current/latest deployment

Removed distribute's, activate's, and rollback's usage of the broker to
get gear groups, replaced with using the new platform GearRegistry to
determine child gears