Commit 4f4c3b13 (v3.3) fixed an issue where performing cleanup of
libvirt objects could sometimes lose error messages, by adding code
to copy the libvirt error into last_error prior to cleanup paths.
However, it caused a regression: on other paths, some errors are now
printed twice, if libvirt still remembers in its thread-local
storage that an error was set even after virsh cleared last_error.
For example:

$ virsh -c test:///default snapshot-delete test blah
error: Domain snapshot not found: no domain snapshot with matching name 'blah'
error: Domain snapshot not found: no domain snapshot with matching name 'blah'

Fix things by telling libvirt to discard any thread-local errors at
the same time virsh prints an error message (whether or not the libvirt
error is the same as what is stored in last_error).

Update the virsh-undefine testsuite (partially reverting portions of
commit b620bdee, by removing -q, to more easily pinpoint which commands
are causing which messages), now that there is only one error message
instead of two.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>