Fix port on interactive login (Fix #12228)

Primary cause was a typo "prt" (which would have been
detected by flake8!) While trying to track this down,
I went ahead and added a more proper regex for the
server string parsing.

/cc @sbesson @khgillen

See https://trac.openmicroscopy.org.uk/ome/ticket/12228 for expected behavior. All other behavior on login should remain as it was before.