For example, passt/dhcp rather than dhcp/passt.  This is more
consistent with the two_guests and other test groups, and makes some
other cleanups simpler.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Put the pieces together to use the new style context based dispatch for
the passt_in_pasta tests.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Convert the pasta and passt tests to use new-style context execution
for the things that run in the "passt" frame.  Don't touch the
passt_in_ns or two_guests tests yet, because they run passt inside a
namespace which introduces some additional complications we have yet
to handle.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

For the passt and passt_in_ns tests we have a "shutdown" testcase that
checks for any errors from the passt process we were using (including
valgrind warnings).  Do the same for pasta tests, so that we catch any
error codes from the pasta process.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

The "valgrind" test cases are designed to pick up errors reported when
passt is running under valgrind.  But what it actually does is just kill
the passt process, then see if it had a non-zero exit code.  That means it
will equally well pick up any other problems which caused passt to exit
with an error status: either something detected within passt or as a result
of passt being killed by an unexpected signal.

The fact that the "valgrind" test is actually responsible for shutting down
the passt process is non-obvious and can lead to problems when selectively
running tests during debugging.

Rename the "valgrind" tests to "shutdown" tests and run it regardless of
whether we're using valgrind or not.  This allows us to remove an ugly
speacial case in the passt_in_ns teardown code.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>