Reasonable error message if network_interface is not found

Change-Id: I96b7af2472addb879df545818a67f58ace8b2572

playbooks/roles/bifrost-ironic-install/tasks/install.yml

@@ -13,6 +13,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 ---
+- name: "Check that the provided interface is defined"
+  fail:
+    msg: >
+      Network interface {{ network_interface }} is not known to Ansible.
+      If you're testing Bifrost on virtual machines, do not forget to invoke
+      "bifrost-cli testenv" or use the "bifrost-create-vm-nodes" role first.
+      If you're using Bifrost on real bare metal, you have to provide the
+      network interface via the "network_interface" variable or the
+      --network-interface argument to "bifrost-cli install".
+  when: ('ansible_' + ans_network_interface) not in hostvars[inventory_hostname]
+
 - name: "Update Package Cache"
   apt: update_cache=yes
   when: ansible_os_family == 'Debian'

playbooks/roles/bifrost-keystone-install/tasks/main.yml

@@ -11,6 +11,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 ---
+- name: "Check that the provided interface is defined"
+  fail:
+    msg: >
+      Network interface {{ network_interface }} is not known to Ansible.
+      If you're testing Bifrost on virtual machines, do not forget to invoke
+      "bifrost-cli testenv" or use the "bifrost-create-vm-nodes" role first.
+      If you're using Bifrost on real bare metal, you have to provide the
+      network interface via the "network_interface" variable or the
+      --network-interface argument to "bifrost-cli install".
+  when: ('ansible_' + ans_network_interface) not in hostvars[inventory_hostname]
+
 # NOTE(cinerama) dummy-defaults.yml is an empty defaults file. We use it
 # here to ensure that with_first_found won't fail should we not have
 # defaults for a particular distribution, version, etc.