client: Only enable logging when we have a parcel name
client: Only enable logging when we have a parcel name

- Enable logging when need_parcel() is called.  Thus, we don't log anything
for non-parcel-specific commands like "isr auth" and "isr ls", all of which
are trivial anyway.

- message(): Don't call message_string() when logging is disabled

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr