Add graceful shutdown when interrupted

If implemented this permit restoring a clean state in case of signal
interruption.

Signed-off-by: Soule BA <soule@weave.works>

cmd/flux/testdata/build-kustomization/delete-service/deployment.yaml

@@ -71,4 +71,4 @@ spec:
             memory: 512Mi
           requests:
             cpu: 100m
-            memory: 64Mi
+            memory: 64Mi

cmd/flux/testdata/build-kustomization/delete-service/hpa.yaml

@@ -17,4 +17,4 @@ spec:
         type: Utilization
         # scale up if usage is above
         # 99% of the requested CPU (100m)
-        averageUtilization: 99
+        averageUtilization: 99

cmd/flux/testdata/build-kustomization/podinfo-kustomization.yaml

@@ -12,4 +12,4 @@ spec:
   sourceRef:
     kind: GitRepository
     name: podinfo
-  targetNamespace: default
+  targetNamespace: default

cmd/flux/testdata/build-kustomization/podinfo-source.yaml

@@ -13,4 +13,4 @@ spec:
   interval: 30s
   ref:
     branch: master
-  url: https://github.com/stefanprodan/podinfo
+  url: https://github.com/stefanprodan/podinfo

cmd/flux/testdata/build-kustomization/podinfo/deployment.yaml

@@ -71,4 +71,4 @@ spec:
             memory: 512Mi
           requests:
             cpu: 100m
-            memory: 64Mi
+            memory: 64Mi

cmd/flux/testdata/build-kustomization/podinfo/hpa.yaml

@@ -17,4 +17,4 @@ spec:
         type: Utilization
         # scale up if usage is above
         # 99% of the requested CPU (100m)
-        averageUtilization: 99
+        averageUtilization: 99

cmd/flux/testdata/build-kustomization/podinfo/service.yaml

@@ -14,4 +14,4 @@ spec:
     - port: 9999
       targetPort: grpc
       protocol: TCP
-      name: grpc
+      name: grpc