mds/Migrator.cc: fix possible NULL pointer dereference

Move dout() calls behind the related asserts to prevent possible NULL
pointer dereference.

CID 717001 (#1 of 1): Dereference null return value (NULL_RETURNS)
  dereference: Dereferencing a pointer that might be null "diri" when calling
  "operator <<(std::ostream &, CInode

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
mds/Migrator.cc: fix dereference NULL return value

CID 717000 (#1 of 2): Dereference null return value (NULL_RETURNS)
  dereference: Dereferencing a pointer that might be null "dir" when
  calling "operator <<(std::ostream &, CDir &)".

CID 717000 (#2 of 2): Dereference null return value (NULL_RETURNS)
  dereference: Dereferencing a pointer that might be null "dir" when
  calling "Migrator::import_reverse_unfreeze(CDir *)".

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
mds/Migrator.cc: fix possible dereference NULL return value

CID 716999 (#1 of 1): Dereference null return value (NULL_RETURNS)
  dereference: Dereferencing a pointer that might be null "in" when
  calling "CInode::put_stickydirs()".

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
mds/Migrator.cc: delete some empty lines at EOF

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
mds/Migrator.cc: fix possible dereference NULL return value

ID 716998 (#1 of 2): Dereference null return value (NULL_RETURNS)
  dereference: Dereferencing a pointer that might be null "in" when
  calling "operator <<(std::ostream &, CInode &)".

CID 716998 (#2 of 2): Dereference null return value (NULL_RETURNS)
  dereference: Dereferencing a pointer that might be null "in" when
  calling "MDCache::add_replica_dir(ceph::buffer::list::iterator &,
  CInode *, int, std::list<Context *, std::allocator<Context *> > &)".

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
mds/Migrator.cc: fix possible dereference NULL return value

CID 716997 (#1 of 1): Dereference null return value (NULL_RETURNS)
  dereference: Dereferencing a pointer that might be null "in" when
  calling "MDSCacheObject::is_auth() const".

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #310 from dalgaaf/wip-da-CID-fixes-4

Reviewed-by: Sage Weil <sage@inktank.com>