join: Fix TypeError when handling exception

join: Fix TypeError when handling exception

When we can't resolve a domain name, we were inadvertently throwing a
TypeError whilst trying to output a helpful message. E.g.

ERROR(<class 'TypeError'>): uncaught exception - 'NTSTATUSError' object
does not support indexing

Instead of indexing the object, we want to index the Exception.args so
that we just display the string portion of the exception error.

The same problem is also present for the domain trust commands.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13747

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Rowland Penny <rpenny@samba.org>
Reviewed-by: Jeremy Allison <rpenny@samba.org>