Don't update cached process cpu info timestamp.
Don't update cached process cpu info timestamp.

In cases when we just return the cached info. That way next time this
cached info is used to calculate cpu utilization, it's calculated over
a correct interval (since when it was actually gathered, not since
when it was returned to the caller).

Change-Id: Iae031cd97174ef163e68ff758394ae62750a0228
Reviewed-on: http://review.couchbase.org/122824
Tested-by: Aliaksey Artamonau <ce14b1c16e0fd654f926118eb8addbec5aff4ffa@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Steve Watanabe <0cfa60539d74abcbbecaf09c76ac8a543ff82c2b@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@couchbase.com>

couchbase/sigar,couchbase/sigar