* client: improve group service stanza interpolation and check_restart support
Interpolation can now be done on group service stanzas. Note that some task runtime specific information
that was previously available when the service was registered poststart of a task is no longer available.
The check_restart stanza for checks defined on group services will now properly restart the allocation upon
check failures if configured.
Some of the context uses in TR hooks are useless (Killed during Stop
never seems meaningful).
None of the hooks are interruptable for graceful shutdown which is
unfortunate and probably needs fixing.
