Merge pull request #1009 from cderici/controller-name-not-found

#1009

#### Description

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

Fixes #996 

#### QA Steps

Testing this requires a bit of stateful actions. I see two easy ways to test:

1. Use the integration test I added. 

Add `import pdb;pdb.set_trace()` right before the `new_cont.connect(` line, and run the integration test with `--pdb` as follows:

```
tox -e integration -- -- tests/integration/test_connection.py::test_connection_happy_path --pdb
```

Before continuing, go find the `controllers.yaml` and rename it to something else (sort of easier than removing juju-cli etc):

```
mv controllers.yaml controllers.yaml.tmp
```

Now continue in the pdb (`c`) to see if the new connection will be established without a problem.

2. Do what the integration test is doing manually in the repl:

```python
 $ python -m asyncio
>>> from juju import controller
>>> c=controller.Controller();await c.connect()
```

Stop at this point to rename the `controllers.yaml` file.

```python
>>> new_c=controller.Controller()
>>> await new_c.connect(endpoint=c.endpoint, username=c.username, password=c.password, cacert=c.cacert)
```

This should succeed.

Don't forget to rename your controllers.yaml back:

```
mv controllers.yaml.tmp controllers.yaml
```

#### Notes & Discussion

JUJU-5317

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

tests/integration/test_connection.py

@@ -24,6 +24,20 @@
 logger = logging.getLogger(__name__)
 
 
+@base.bootstrapped
+@pytest.mark.asyncio
+async def test_connection_happy_path(event_loop):
+    async with base.CleanController() as contr:
+        conn = contr.connection()
+        new_cont = Controller()
+        await new_cont.connect(endpoint=conn.endpoint,
+                               username=conn.username,
+                               password=conn.password,
+                               cacert=conn.cacert,
+                               )
+        await new_cont.disconnect()
+
+
 @base.bootstrapped
 @pytest.mark.asyncio
 async def test_monitor(event_loop):