mds: Fix Dumper::undump (missing lock)

Two problems were causing undump to fail:
* Objecter lock was not being taken around call to
  .write() and .write_full() calls, causing assertion.
* Once that is fixed, it is necessary to use a separate,
  local lock to protect the completion condition for
  write operations

Signed-off-by: John Spray <john.spray@inktank.com>
mds: Add LogEvent::str_to_type

For cephfs-journal-tool to resolve user input to a EVENT_* constant

Signed-off-by: John Spray <john.spray@inktank.com>
mds: switch __u32 with LogEvent::EventType typedef

Signed-off-by: John Spray <john.spray@inktank.com>
mds: Add EMetaBlob::get_dentries

For tools that would like to know which dentries are
touched by a metablob, without understanding its
internal format.

Signed-off-by: John Spray <john.spray@inktank.com>
mds: Add getter for EMetablob.client_name

Signed-off-by: John Spray <john.spray@inktank.com>
mds: add getter for ESession.client_inst

Signed-off-by: John Spray <john.spray@inktank.com>
tools: Create cephfs-journal-tool

This is for debugging/repairing CephFS journals.

Signed-off-by: John Spray <john.spray@inktank.com>
rpm: add cephfs-journal-tool to RPM build

Signed-off-by: John Spray <john.spray@inktank.com>
debian: add cephfs-journal-tool to ceph-mds

Signed-off-by: John Spray <john.spray@inktank.com>
gitignore: Add cephfs-journal-tool

Signed-off-by: John Spray <john.spray@inktank.com>
docs: Add cephfs-journal-tool

Signed-off-by: John Spray <john.spray@inktank.com>