crush, mon: bump up map version only if we truly created a weight-set

crush, mon: bump up map version only if we truly created a weight-set

In crush-compat mode mgr/balancer will do 'ceph osd crush weight-set create-compat'
on each call to 'ceph balancer optimize <plan>', which turns out to be
bumping up osdmap version without modifying anything (we haven't executed the
plan yet).

E.g.:
./bin/ceph balancer reset && ./bin/ceph balancer optimize crush test && ./bin/ceph balancer show crush
// starting osdmap epoch 993
// starting crush version 962
// mode crush-compat

./bin/ceph balancer reset && ./bin/ceph balancer optimize crush test && ./bin/ceph balancer show crush
// starting osdmap epoch 994
// starting crush version 963
// mode crush-compat

Fix the above problem by checking whether a new weight-set is truly created or not
on the OSDMonitor-side.

Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>