LU-10383 hsm: refactor mdt_coordinator_cb()

LU-10383 hsm: refactor mdt_coordinator_cb()

Split the ARS_WAITING and ARS_STARTED cases of mdt_coordinator_cb()
into subfunctions, mdt_cdt_waiting_cb() and mdt_cdt_started_cb().

Test-Parameters: trivial testlist=sanity-hsm
Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I734e10e4db72f76a6b0de76c383ad0b03efd76d8
Reviewed-on: https://review.whamcloud.com/30552
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>