test-tool: Don't use static binary helper program, nor ISO.

test-tool: Don't use static binary helper program, nor ISO.

This simplifies the libguestfs-test-tool program down to essentials.
Bugs most commonly occur when starting the appliance, so what we
should concentrate on test is just that.

Previously the test tool built a special static binary helper program,
packaged it up in an ISO, then ran this inside the appliance.  None of
this really tested useful failure modes, but they did make the test
tool itself harder to build, harder for users to run, and more
brittle.

This change also adds some more debugging of libguestfs state.