The error path for context initialization is not consistent. Cleanup all
resources on failure.

Removed unused variable user_event_mask.

Add the _BASE_FAILED bit to the event flags so that a base context can
notify waiting sub contexts that they cannot continue.

Running out of sub contexts is an EBUSY result, not EINVAL.
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>