MB-9322 Fix the high idle cpu usage in GIO manager

The existing sleep time of flusher of 0.1s turned out to be too
low and resulted in a lot of wasted cycles during idle time
Set all min sleep and wake times to 2.0 seconds

Also use SingleThreadedRCPtr instead of RCPtr in GIO manager to avoid
the overhead of spin locks

Fix verified using oprofile and top

Change-Id: Ia013b93a57225b42c48df47e3b465b1067478cf4
Reviewed-on: http://review.couchbase.org/29593
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>