Port of #9584

Fixes #9583

lib/private/group/metadata.php: For subadmins also return an array of groups, indexed by their GIDs.
settings/users.php: Convert array of arrays to array of GIDs before calling into OC_Group::displayNamesInGroups.

Signed-off-by: Stephan Peijnik <speijnik@anexia-it.com>

Fix indentation.

Signed-off-by: Stephan Peijnik <speijnik@anexia-it.com>

Renamed $grp to $group in foreach loop.

Signed-off-by: Stephan Peijnik <speijnik@anexia-it.com>

Use is_null() instead of empty() when checking the return value of GroupManager::get().

Additionally, $grp was renamed to $group inside
 \OC\Group\MetaData::fetchGroups().

Signed-off-by: Stephan Peijnik <speijnik@anexia-it.com>

Updated code to reflect changes introduced to \OC\Group\MetaData.

Now that fetchGroups() does not exist anymore and getGroups() is called
directory, the 'groups' property does not exist anymore.
Instead, we now generate that array on the fly and return it from getGroups.

Signed-off-by: Stephan Peijnik <speijnik@anexia-it.com>