osd: make *Force* functions public

osd: make *Force* functions public

Otherwise you'll have 'protected' errors:
home/jenkins/workspace/ceph-master/src/osd/OSD.cc:8518:12: error: 'UnsetForceBackfill' is a protected member of 'PG'
              PG::UnsetForceBackfill())));
                  ^
/home/jenkins/workspace/ceph-master/src/osd/PG.h:1902:16: note: declared protected here
  TrivialEvent(UnsetForceBackfill)
               ^
/home/jenkins/workspace/ceph-master/src/osd/OSD.cc:8525:12: error: 'SetForceBackfill' is a protected member of 'PG'
              PG::SetForceBackfill())));
                  ^
/home/jenkins/workspace/ceph-master/src/osd/PG.h:1901:16: note: declared protected here
  TrivialEvent(SetForceBackfill)
               ^
/home/jenkins/workspace/ceph-master/src/osd/OSD.cc:8534:12: error: 'UnsetForceRecovery' is a protected member of 'PG'
              PG::UnsetForceRecovery())));
                  ^
/home/jenkins/workspace/ceph-master/src/osd/PG.h:1900:16: note: declared protected here
  TrivialEvent(UnsetForceRecovery)
               ^
/home/jenkins/workspace/ceph-master/src/osd/OSD.cc:8541:12: error: 'SetForceRecovery' is a protected member of 'PG'
              PG::SetForceRecovery())));
                  ^
/home/jenkins/workspace/ceph-master/src/osd/PG.h:1899:16: note: declared protected here
  TrivialEvent(SetForceRecovery)
               ^
4 errors generated.

Signed-off-by: Willem Jan Withagen <wjw@digiware.nl>