Pin build.lock for all layers to the commit hash

The build.lock branch points to master which means that the layer is not
locked.  Lock the layers to the commit hash instead; this ensures
reproducible builds as much as possible.

Change-Id: Ica9a1d7235a3d23e02f8e10dfcf5352ea7a705ed

charmcraft.yaml

@@ -13,7 +13,7 @@ parts:
       - libmysqlclient-dev  # for executable mysql_shell 
     override-build: |
       apt-get install ca-certificates -y
-      tox -e add-build-lock-file
+      tox -e build-reactive
     override-stage: |
       echo "Copying charm to staging area: $CHARMCRAFT_STAGE"
       NAME=$(ls $CHARMCRAFT_PART_BUILD/build/builds)

src/build.lock

@@ -5,7 +5,7 @@
       "item": "layer:options",
       "url": "https://github.com/juju-solutions/layer-options.git",
       "vcs": null,
-      "branch": "refs/heads/master",
+      "branch": "fcdcea4e5de3e1556c24e6704607862d0ba00a56",
       "commit": "fcdcea4e5de3e1556c24e6704607862d0ba00a56"
     },
     {
@@ -13,7 +13,7 @@
       "item": "layer:basic",
       "url": "https://github.com/juju-solutions/layer-basic.git",
       "vcs": null,
-      "branch": "refs/heads/master",
+      "branch": "a3ff62c32c993d80417f6e093e3ef95e42f62083",
       "commit": "a3ff62c32c993d80417f6e093e3ef95e42f62083"
     },
     {
@@ -21,7 +21,7 @@
       "item": "layer:openstack",
       "url": "https://github.com/openstack/charm-layer-openstack",
       "vcs": null,
-      "branch": "refs/heads/master",
+      "branch": "207bac8bec837edc6a4d6003f51d5b59d2d75adb",
       "commit": "207bac8bec837edc6a4d6003f51d5b59d2d75adb"
     },
     {
@@ -37,7 +37,7 @@
       "item": "interface:tls-certificates",
       "url": "https://github.com/juju-solutions/interface-tls-certificates",
       "vcs": null,
-      "branch": "refs/heads/master",
+      "branch": "d9850016d930a6d507b9fd45e2598d327922b140",
       "commit": "d9850016d930a6d507b9fd45e2598d327922b140"
     },
     {
@@ -45,7 +45,7 @@
       "item": "interface:dashboard-plugin",
       "url": "https://github.com/openstack/charm-interface-dashboard-plugin.git",
       "vcs": null,
-      "branch": "refs/heads/master",
+      "branch": "06031deac8b37e912dc69f1c6d2e2634696d2547",
       "commit": "06031deac8b37e912dc69f1c6d2e2634696d2547"
     },
     {