handle empty and missing configuration file.

 + without immediately dying
 * correctly clear config_file_t to NULL
 * reduce minor parse errors from Crit to Warn
 * fix several incorrect err_types
 * gracefully return after missing sub-nodes and trees
 * for LOG block, allow empty as well as harmless!

Signed-off-by: William Allen Simpson <bill@cohortfs.com>
Acked-by: Jim Lieb <lieb@sea-troll.net>
Consolidate FSAL initiation into fsal_manager

In order to have a DS {} block with a FSAL {} block in it,
reshuffle some of the FSAL functions that were in various
files into include/fsal.h and FSAL/fsal_manager.c, as
fsal_load_init() is the only caller of load_fsal() there.

Merge name length testing into fsal_load_init().

Rename struct fsal_args to match struct subfsal_args.
Reorder struct subfsal_args to match struct fsal_args.

Signed-off-by: William Allen Simpson <bill@cohortfs.com>
Acked-by: Jim Lieb <lieb@sea-troll.net>