b=21420 Add mds/mgs stats to HEAD

b=21420 Add mds/mgs stats to HEAD

1)remove useless counter from mds and move some definitions from mds to mdt;
2)move LPROCFS_MD_OP_INITs from lprocfs_alloc_md_stats() to
  lprocfs_init_mps_stats(), which is needed by this stats;
3)increase mdt counter for each type operation

i=andreas
i=wangdi