MB-21777: max_cas_str not formatting on Linux

MB-21777: max_cas_str not formatting on Linux

Seems an issue with snprintf where we use timeString as input and
output yields only the nanosecond fractions being printed.

Fix also reduces buffers down, they're still bigger than we need, but
100 is way too much.

Change-Id: Ief6755d15d4d77a10a6c14fb76321893a7dd0d9c
Reviewed-on: http://review.couchbase.org/70298
Reviewed-by: David Haikney <david.haikney@couchbase.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>