Make ansible version configurable

Currently the default ansible version is selected by the version of
zuul itself. However we want to make this configurable per deployment
(zuul.conf), tenant and job.

Change-Id: Iccbb124ac7f7a8260c730fbc109ccfc1dec09f8b

zuul/lib/ansible.py

@@ -123,13 +123,18 @@ class ManagedAnsible:
 class AnsibleManager:
     log = logging.getLogger('zuul.ansible_manager')
 
-    def __init__(self, zuul_ansible_dir=None):
+    def __init__(self, zuul_ansible_dir=None, default_version=None):
         self._supported_versions = {}
         self.default_version = None
         self.zuul_ansible_dir = zuul_ansible_dir
 
         self.load_ansible_config()
 
+        # If configured, override the default version
+        if default_version:
+            self.requestVersion(default_version)
+            self.default_version = default_version
+
     def load_ansible_config(self):
         c = resource_string(__name__, 'ansible-config.conf').decode()
         config = configparser.ConfigParser()
@@ -193,17 +198,30 @@ class AnsibleManager:
             raise Exception('Requested ansible version %s not found' % version)
         return ansible
 
-    def getAnsibleCommand(self, version=None, command='ansible-playbook'):
+    def getAnsibleCommand(self, version, command='ansible-playbook'):
         ansible = self._getAnsible(version)
         return os.path.join(ansible.venv_path, 'bin', command)
 
-    def getAnsibleDir(self, version=None):
+    def getAnsibleDir(self, version):
         ansible = self._getAnsible(version)
         return os.path.join(self.zuul_ansible_dir, ansible.version)
 
-    def getAnsiblePluginDir(self, version=None):
+    def getAnsiblePluginDir(self, version):
         return os.path.join(self.getAnsibleDir(version), 'zuul', 'ansible')
 
+    def requestVersion(self, version):
+        if version not in self._supported_versions:
+            raise Exception(
+                'Requested ansible version \'%s\' is unknown. Supported '
+                'versions are %s' % (
+                    version, ', '.join(self._supported_versions)))
+
+    def getSupportedVersions(self):
+        versions = []
+        for version in self._supported_versions:
+            versions.append((version, version == self.default_version))
+        return versions
+
     def copyAnsibleFiles(self):
         if os.path.exists(self.zuul_ansible_dir):
             shutil.rmtree(self.zuul_ansible_dir)