virshtest: Reimplement 'virsh-output' test

virshtest: Reimplement 'virsh-output' test

Adapt the 'tests/virsh-output-commands' file from 'virsh-output' test as
a source. Apart from expanding the bash function to each command, I've
also had to drop the negative tests for argument population, as a
command parsing error aborts the execution of the script right away
rather than just reporting the error.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>