test: Create common state directories for temporary files

The test scripts create a bunch of temporary files to keep track of
internal state.  Some are made in /tmp with individual mktemp calls, some
go in the passt source directory, and some go in $LOGDIR.  This can
sometimes make it messy to clean up after failed test runs.

Start cleaning this up by creating a single "state" directory ($STATEBASE)
in /tmp for all the state or temporary files used by a single test run.
Clean it up automatically in cleanup() - except when DEBUG==1, because
those files can be useful for debugging test script failures.

We create subdirectories under $STATEBASE for each setup function, exposed
as $STATESETUP.  We also create subdirectories for each test script and
expose those to the scripts as __STATEDIR__.

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

test/run

@@ -48,6 +48,7 @@ COMMIT="$(git log --oneline --no-decorate -1)"
 
 # cleanup() - Remove temporary files
 cleanup() {
+	[ ${DEBUG} -eq 1 ] || rm -rf "${STATEBASE}"
 	rm -f /tmp/.passt_test_log_pipe
 }
 
@@ -176,6 +177,7 @@ else
 	rm -rf "${LOGDIR}"
 	mkdir -p "${LOGDIR}"
 	:> "${LOGFILE}"
+	STATEBASE="$(mktemp -d --tmpdir passt-tests-XXXXXX)"
 	trap "cleanup" EXIT
 	run_term
 fi