qa/suites/rados/multimon: skew clocks 2s (< paxos lease)

qa/suites/rados/multimon: skew clocks 2s (< paxos lease)

If the leader is the one with the accurate clock, it can still
form quorum, but if the leader has the skewed clock, all other mons appear
skewed from its perspective and no quorum is formed.  This leads to
intermittent failures, depending on the non-deterministic teuthology
deployment order and how the mon IPs sort.

Fix by reducing the skew.  This is enough skew to trigger a warning, but
not enough that it will break quorum.  This ensures that the parts of the
teuthology test that issue random mon commands won't fail (e.g., 'ceph osd
dump').

Fixes: http://tracker.ceph.com/issues/40112
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit fd00136eb3b181ca34937fc7ea99427338ae6069)