Cache static values in the logger

The pid won't change for memcached for the duration of the
process lifetime, so there is no point of doing a function call
to get it each time. The likelyhood of a hostname change is also
really small and not worth the extra system call every time we
want to insert an event (could be thousand per sec)

Change-Id: I823c4f500d2b154d4086a3ee95f522dd04f6ee60
Reviewed-on: http://review.couchbase.org/41791
Reviewed-by: Daniel Owen <owend@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>