testing: Fix loading test config for tests that were never run

The file won't exist in the previous location until load-testconfig was
executed once.  Since it's not modified by the script it's fine to
load it directly from the original location.

Fixes: a103f3a284 ("testing: Add options to only run pre- or posttest scripts of a scenario")

testing/do-tests

@@ -362,7 +362,7 @@ do
 	unset DBHOSTS
 	unset IPV6
 	unset SWANCTL
-	source $TESTDIR/test.conf
+	source $DEFAULTTESTSDIR/${testname}/test.conf
 
 	DBDIR=/etc/db.d
 	STATUS="passed"