testenv: Support test overlaying a directory to look for templates

This way tests which require a very specific config file can override
specific template files used by object classes.

Change-Id: I65d1b1e826d2d430ee83810d998b98d0ccaa07cd
diff --git a/selftest/suite_test/suitedirB/suiteC/suite.conf b/selftest/suite_test/suitedirB/suiteC/suite.conf
new file mode 100644
index 0000000..44be3fc
--- /dev/null
+++ b/selftest/suite_test/suitedirB/suiteC/suite.conf
@@ -0,0 +1,6 @@
+resources:
+  ip_address:
+  - addr: 10.42.42.2 # stp
+
+defaults:
+  timeout: 60s