MB-31581: Cast nanoseconds.count() to int64_t for checked_snprintf
MB-31581: Cast nanoseconds.count() to int64_t for checked_snprintf

This fix casts nanoseconds.count() to an int64_t and changes the
expected format specifier to account for multiple operating systems.
This fixes the warning raised by the CB_FORMAT_PRINTF check.

Change-Id: Icad53eb4aee9967c249878c634f925ef725710b8
Reviewed-on: http://review.couchbase.org/100464
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Daniel Owen <b3fc0e1a51f252986e60be7da121b74d3ac6845f@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine