Add a tox environment ansible-syntax for checking ansible syntax

Run this environment in TravisCI.

.travis.yml

@@ -22,6 +22,8 @@ env:
     - TOX_ENV=docs
     # Run python2.7 unit tests.
     - TOX_ENV=py27
+    # Run ansible syntax checks.
+    - TOX_ENV=ansible-syntax
 
 install:
   # Install a virtualenv for tox.

tox.ini

@@ -37,6 +37,26 @@ commands = oslo_debug_helper {posargs}
 [testenv:alint]
 commands = ansible-lint ansible/*.yaml
 
+[testenv:ansible-syntax]
+commands =
+    # Install ansible role dependencies from Galaxy.
+    ansible-galaxy install \
+        -r {toxinidir}/requirements.yml \
+        -p {toxinidir}/ansible/roles
+    # Perform an Ansible syntax check. Skip some playbooks which require extra
+    # variables to be defined.
+    bash -c \
+        "ansible-playbook \
+        --connection=local \
+        --syntax-check \
+        --list-tasks \
+        $(find {toxinidir}/ansible \
+            -maxdepth 1 \
+            -name '*.yml' \
+            -not -name idrac-bootstrap-one.yml \
+            -not -name idrac-bootstrap.yml) \
+        {posargs}"
+
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.