osd/OSDMap: skip out/crush-out osds

osd/OSDMap: skip out/crush-out osds

We might do 'ceph osd out <osd.x>' or 'ceph osd crush reweight <osd.x> 0'
for various reasons, and hence can produce 0-weighted OSDs.
Skip those OSDs when trying to calculdate PG upmaps so we won't be able to
hit the *assert* below:

/build/ceph-13.0.1-2232-g64665c7/src/osd/OSDMap.cc: 4179: FAILED assert(target > 0)

See also:

http://pulpito.ceph.com/xxg-2018-02-28_09:02:53-rados-wip-fix-upmap-distro-basic-smithi/2235497/

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