hook context id overly verbose

[John A Meinel]

Every time a charm invokes a hook tool, we drop cruft at DEBUG level:
unit-easyrsa-0: 12:16:36 DEBUG worker.uniter.jujuc hook context id "easyrsa/0-update-status-9028046492320369901"; dir "/var/lib/juju/agents/unit-easyrsa-0/charm"
unit-easyrsa-0: 12:16:36 DEBUG worker.uniter.jujuc hook context id "easyrsa/0-update-status-9028046492320369901"; dir "/var/lib/juju/agents/unit-easyrsa-0/charm"
unit-easyrsa-0: 12:16:36 DEBUG worker.uniter.jujuc hook context id "easyrsa/0-update-status-9028046492320369901"; dir "/var/lib/juju/agents/unit-easyrsa-0/charm"
unit-easyrsa-0: 12:16:36 DEBUG worker.uniter.jujuc hook context id "easyrsa/0-update-status-9028046492320369901"; dir "/var/lib/juju/agents/unit-easyrsa-0/charm"
unit-easyrsa-0: 12:16:37 DEBUG worker.uniter.jujuc hook context id "easyrsa/0-update-status-9028046492320369901"; dir "/var/lib/juju/agents/unit-easyrsa-0/charm"

Note that this isn't the interesting bit at all.
    logger.Tracef("running hook tool %q %q", req.CommandName, req.Args)
    logger.Tracef("running hook tool %q", req.CommandName)
    logger.Debugf("hook context id %q; dir %q", req.ContextId, req.Dir)

It seems we dropped the interesting ones to Trace, but then left the uninteresting one at Debug.