LU-17431 nodemap: determine if nodemap is currently loading

LU-17431 nodemap: determine if nodemap is currently loading

To control operations on dynamic nodemaps, we need to know if the
current nodemap configuration is in the process of being loaded.
Only once it is fully loaded the nodemap_mgs() function returns true.
So change semantic of global variable nodemap_config_loaded, to be:
* 0: not loaded yet
* 1: successfully loaded
* -1: loading in progress

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: If5e52e924415f644d0134f4093c2405df0887f87
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55001
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>