Bug 1600116: Validate group shortname across all institutions.
Validate that the group shortname is unique across all institutions instead of just the institution that is being processed. Make sure the mandatory fields (shortname, displayname, roles) in the upload csv are not empty as the group shortname validation relies on the display name. Also, improve the error message thrown during the submit when the groupname is not unique. behatnotneeded Change-Id: I23278de9bb52f1289535924f1accf3fcb9d559ce