Integration test for metrics + bug fix

This commit:
- adds the beginnings of an integration testing framework
- adds an integration test to exercise metric collection
- adds a test charm with metrics collection
- fixes a potential bug that can cause N2VC to fail if no
initial-config-primitive is specified in the VNF descriptor

Signed-off-by: Adam Israel <adam.israel@canonical.com>
diff --git a/tests/charms/layers/metrics-ci/metadata.yaml b/tests/charms/layers/metrics-ci/metadata.yaml
new file mode 100755
index 0000000..060274d
--- /dev/null
+++ b/tests/charms/layers/metrics-ci/metadata.yaml
@@ -0,0 +1,12 @@
+name: metrics-ci
+summary: <Fill in summary here>
+maintainer: Adam Israel <Adam.Israel@ronin>
+description: |
+  <Multi-line description here>
+tags:
+  # Replace "misc" with one or more whitelisted tags from this list:
+  # https://jujucharms.com/docs/stable/authors-charm-metadata
+  - misc
+subordinate: false
+series:
+  - xenial