Now that portals_handle_ops contains only a char*,
it is functioning primarily to identify the owner of each handle.
So change the name to h_owner, and the type to const char*.

Note: this h_owner is now quite different from the similar h_owner
in the server code.  When server code it merged the
"med" pointer should be stored in the "mfd" and validated separately.

Change-Id: Ie2e9134ea22c4929683c84bf45c41b96b348d0a2
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-on: https://review.whamcloud.com/35798


Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>