virshtest: Prepare for simpler testing - echo tests

virshtest: Prepare for simpler testing - echo tests

Embedding the expected output in a C source code makes it very hard to
extend tests. In order to be able to test the outputs against data in
files on disk we need better naming of the tests themselves.

Use virTestCounterNext/Reset with appropriate tags to give reasonable
names to the 'virsh echo' tests' and prepare the 'DO_TEST' macro for
wider use.

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