LU-4705 mdc: improve mdc_enqueue() error message

LU-4705 mdc: improve mdc_enqueue() error message

Include the parent/child FIDs and name in the mdc_enqueue()
debug message.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I7b84921a52a4650be70fe87eea691ba2217bb3a6
Reviewed-on: https://review.whamcloud.com/28978
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Steve Guminski <stephenx.guminski@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>