LU-12137 osd-ldiskfs: create locked and unlocked versions of osd lookup code

LU-12137 osd-ldiskfs: create locked and unlocked versions of osd lookup code

The inode_lock is expected to be taken when lookup_one_len() is
called. Rename osd_ios_lookup_one_len() to osd_lookup_one_len()
since it now doesn't take the inode_lock manually. Instead it
expects the called to have already called inode_lock(). The
osd_lookup_one_len_unlocked() function will always take the
inode_lock itself. Currently osd-ldiskfs always uses
osd_lookup_one_len_unlocked().

Change-Id: Ie406db5e24f983e52ea8a89bca66546ab9d25148
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/35594
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>