test: replace gtester with a TAP driver

gtester is deprecated by upstream glib (see for example the announcement
at https://blog.gtk.org/2018/07/11/news-from-glib-2-58/

) and it does
not support tests that call g_test_skip in some glib stable releases.

glib suggests instead using Automake's TAP support, which gtest itself
supports since version 2.38 (QEMU's minimum requirement is 2.40).
We do not support Automake, but we can use Automake's code to beautify
the TAP output.  I chose to use the Perl copy rather than the shell/awk
one, with some changes so that it can accept TAP through stdin, in order
to reuse Perl's TAP parsing package.  This also avoids duplicating the
parser between tap-driver.pl and tap-merge.pl.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1543513531-1151-3-git-send-email-pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>