virshtest: Add support for testing commands read from input file and adapt alias...

virshtest: Add support for testing commands read from input file and adapt alias tests

Add support for reading a file and passing it to virsh in 'batch' mode
so that multiple commands can be easily tested with one invocation of
virsh.

To show how it's used adapt the alias handling tests to be invoked all
at once.

As in batch mode the arguments are read from a string and separated
inside virsh, one test is kept separate to be parsed in argv mode.

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