Remove dependency to juju cli for controller_name

controllers.yaml is read for the controller_name after a connection is
established, and this creates a depends on the juju-cli to be
installed in the system, which is not required for pylibjuju.

juju/client/connector.py

@@ -9,7 +9,7 @@
 from juju.client.gocookies import GoCookieJar, go_to_py_cookie
 from juju.client.jujudata import FileJujuData, API_ENDPOINTS_KEY
 from juju.client.proxy.factory import proxy_from_config
-from juju.errors import JujuConnectionError, JujuError, PylibjujuProgrammingError
+from juju.errors import JujuConnectionError, JujuError, PylibjujuProgrammingError, ControllerNameNotFound
 from juju.client import client
 
 log = logging.getLogger('connector')
@@ -97,7 +97,11 @@ async def connect(self, **kwargs):
         if not self.controller_name:
             if 'endpoint' not in kwargs:
                 raise PylibjujuProgrammingError("Please report this error to the maintainers.")
-            self.controller_name = self.jujudata.controller_name_by_endpoint(kwargs['endpoint'])
+            try:
+                self.controller_name = self.jujudata.controller_name_by_endpoint(kwargs['endpoint'])
+            except ControllerNameNotFound:
+                # It's ok because we might not have the juju cli (controllers.yaml)
+                pass
 
         # Check if we support the target controller
         if not self._connection.info['server-version'].startswith(SUPPORTED_JUJU_API_PREFIX):

juju/client/jujudata.py

@@ -10,7 +10,7 @@
 import yaml
 from juju import tag
 from juju.client.gocookies import GoCookieJar
-from juju.errors import JujuError, PylibjujuProgrammingError
+from juju.errors import JujuError, PylibjujuProgrammingError, ControllerNameNotFound
 from juju.utils import juju_config_dir
 
 API_ENDPOINTS_KEY = 'api-endpoints'
@@ -133,7 +133,11 @@ def controller_name_by_endpoint(self, endpoint):
 
         :param str endpoint: The endpoint of the controller we're looking for
         """
-        for controller_name, controller in self.controllers().items():
+        try:
+            contrs = self.controllers()
+        except FileNotFoundError:
+            raise ControllerNameNotFound()
+        for controller_name, controller in contrs.items():
             if isinstance(endpoint, str):
                 if endpoint in controller[API_ENDPOINTS_KEY]:
                     return controller_name

juju/errors.py

@@ -118,3 +118,7 @@ class JujuModelConfigError(JujuConfigError):
 
 class AbstractMethodError(Exception):
     pass
+
+
+class ControllerNameNotFound(Exception):
+    pass