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: I9a162c7ac182f5657fb8745c07ab484470baa49d

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:manila-plugin",
       "url": "https://github.com/openstack/charm-interface-manila-plugin",
       "vcs": null,
-      "branch": "refs/heads/master",
+      "branch": "14cb348a09b30c92de89878c58e790779ebdad23",
       "commit": "14cb348a09b30c92de89878c58e790779ebdad23"
     },
     {