LU-8993 utils: Use absolute pathname for debug_daemon log file

LU-8993 utils: Use absolute pathname for debug_daemon log file

The lctl debug_daemon command is changed to always provide an
absolute pathname to the kernel.  The kernel code will return EINVAL
if the pathname does not begin with '/', leading to the confusing
error "Invalid argument". This patch allows the user to provide a
relative pathname to the command without generating this error.

The absolute_path function has been moved to string.c and renamed to
cfs_abs_path, so that it may be used by all utilities.

Signed-off-by: Steve Guminski <stephenx.guminski@intel.com>
Change-Id: I35af242bfcfcb9a56135aeabe0423e28e9634bab
Reviewed-on: https://review.whamcloud.com/25485
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>