osd/OSDMap: apply both pg_upmap and pg_upmap_items

osd/OSDMap: apply both pg_upmap and pg_upmap_items

This allows a more flexible upmap policy by combinating
both pg_upmap and pg_upmap_items.

For example:
./bin/ceph osd pg-upmap 1.0 1 2 3
set 1.0 pg_upmap mapping to [1,2,3]

./bin/ceph osd pg-upmap-items 1.0 1 5
set 1.0 pg_upmap_items mapping to [1->5]

 ./bin/ceph pg ls-by-pool cephfs_data_a
PG_STAT OBJECTS MISSING_ON_PRIMARY DEGRADED MISPLACED UNFOUND BYTES LOG DISK_LOG STATE        STATE_STAMP                VERSION REPORTED UP      UP_PRIMARY ACTING  ACTING_PRIMARY
1.0           0                  0        0         0       0     0   0        0 active+clean 2017-07-10 11:04:53.955681     0'0    22:13 [5,2,3]          5 [5,2,3]              5

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