Add 'retry_interval' string setting for CNTL_RETRY_INTERVAL
Add 'retry_interval' string setting for CNTL_RETRY_INTERVAL

This can be used to adjust the retry interval for all types of retries.
This commit makes this setting accessible via a string setting

Change-Id: Ifa384de4d427335e223602d84ccfdb18b6f64c23
Reviewed-on: http://review.couchbase.org/58390
Reviewed-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

avsej/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,mody/libcouchbase,couchbase/libcouchbase,mody/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,avsej/libcouchbase,mody/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,mody/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,avsej/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase