admin: Use the connection to determine a client is connected readonly

admin: Use the connection to determine a client is connected readonly

Prior to this change, we relied solely on the inherited readonly
attribute of a service's socket. This only worked for our UNIX sockets
(and only to some degree), but doesn't work for TCP sockets which are RW
by default, but such connections support RO as well. This patch forces
an update on the client object once we have established a connection to
reflect the nature of the connection itself rather than relying on the
underlying socket's attributes.
Clients connected to the admin server have always been connected as RW
only.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1524399
Signed-off-by: Erik Skultety <eskultet@redhat.com>