virsh: don't reject undefine on active domain

The public API documents that undefine may be used to transition a
running persistent domain into a transient one.  Many drivers still
do not support this usage, but virsh shouldn't be getting in the
way of those that do support it.

This also drops a redundant conditional; vshCommandOptString
guaranteed that name was non-NULL.

* tools/virsh.c (cmdUndefine): Allow undefine on active domains;
the drivers may still reject it, but it is a valid API usage.
* tests/undefine (error): Fix the test to match.

tests/undefine

@@ -1,7 +1,7 @@
 #!/bin/sh
 # exercise virsh's "undefine" command
 
-# Copyright (C) 2008-2009 Red Hat, Inc.
+# Copyright (C) 2008-2009, 2011 Red Hat, Inc.
 
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -30,6 +30,7 @@ fi
 fail=0
 
 # Attempt to undefine a running domain, by domain name.
+# Although the API allows this, the test hypervisor does not.
 $abs_top_builddir/tools/virsh -q -c test:///default undefine test > out 2>&1
 test $? = 1 || fail=1
 cat <<\EOF > exp || fail=1
@@ -38,12 +39,12 @@ error: internal error Domain 'test' is still running
 EOF
 compare exp out || fail=1
 
-# A different diagnostic when specifying a domain ID
+# A similar diagnostic when specifying a domain ID
 $abs_top_builddir/tools/virsh -q -c test:///default undefine 1 > out 2>&1
 test $? = 1 || fail=1
 cat <<\EOF > exp || fail=1
-error: a running domain like 1 cannot be undefined;
-to undefine, first shutdown then undefine using its name or UUID
+error: Failed to undefine domain 1
+error: internal error Domain 'test' is still running
 EOF
 compare exp out || fail=1