LU-1095 mdc: remove console spew from mdc_ioc_fid2path

LU-1095 mdc: remove console spew from mdc_ioc_fid2path

In some cases with a very long pathname, such as with sanity.sh
test_154c, mdc_ioc_fid2path() would spew long debug messages to
the log, because libcfs_debug_vmsg2() refuses to log messages over
one page in size.

Truncate the debug message to only log the last 512 characters
of the pathname, which is sufficient for most debugging, saves a
bit of space in the debug log, and will prevent the debug logging
from printing to the console in the first place.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I3cad19d02e8065574b8baf5694e9894e43112318
Reviewed-on: http://review.whamcloud.com/17078
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>