Repository: rasahq/rasa
Issue: Rasa v1.0 missing detailed logs like previous versions

<!-- THIS INFORMATION IS MANDATORY - YOUR ISSUE WILL BE CLOSED IF IT IS MISSING. If you don't know your Rasa version, use `rasa --version`. 
Please format any code or console output with three ticks ``` above and below.
If you are asking a usage question (e.g. "How do I do xyz") please post your question on https://forum.rasa.com instead -->

**Rasa version**: 1.1.3

**Rasa X version** (if used & relevant): N/A

**Python version**: 3.6.6

**Operating system** (windows, osx, ...): Windows 10

**Issue**:
After upgrading to Rasa v1.0.x, logs outputted to `rasa_core.log` are missing any additional output that appears in the shell/server.

**Error (including full traceback)**:
Currently the log only ever displays:
```
2019-07-12 12:00:20,917 [DEBUG]  Available web server routes: 
/webhooks/rest                                     GET                            custom_webhook_RestInput.health
/webhooks/rest/webhook                             POST                           custom_webhook_RestInput.receive
```

When before, they'd look something like this:
```
Rasa process starting
Added 'nlp_spacy' to component cache. Key 'nlp_spacy-en'.
Available web server routes: 
static                                             GET, OPTIONS, HEAD             /static/[filename]
custom_webhook_RestInput.health                    GET, OPTIONS, HEAD             /webhooks/rest/
custom_webhook_RestInput.receive                   OPTIONS, POST                  /webhooks/rest/webhook
Rasa Core server is up and running on http://localhost:5002
Creating a new tracker for id 'test'.
Received user message 'hi' with intent '{'name': 'greet', 'confidence': 0.6400831082282148}' and entities '[]'
Logged UserUtterance - tracker now has 2 events
Current slot values: 
	target: None
	target_found: None
	user: None
Current tracker state [None, {}, {'prev_action_listen': 1.0, 'intent_greet': 1.0}]
There is a memorised next action '23'
There is no active form
Predicted next action using policy_2_MemoizationPolicy
Predicted next action 'action_identify_user' with prob 1.00.
Calling action endpoint to run action 'action_identify_user'.
Action 'action_identify_user' ended with events '['SlotSet(key: user, value: test)']'
Current tracker state [{}, {'prev_action_listen': 1.0, 'intent_greet': 1.0}, {'slot_user_0': 1.0, 'prev_action_identify_user': 1.0, 'intent_greet': 1.0}]
There is no memorised next action
There is no active form
Predicted next action using policy_0_KerasPolicy
Predicted next action 'utter_greet' with prob 1.00.
Action 'utter_greet' ended with events '[]'
Bot utterance 'BotUttered(text: Hi test, data: {
  "elements": null,
  "buttons": null,
  "attachment": null
})'
Current tracker state [{'prev_action_listen': 1.0, 'intent_greet': 1.0}, {'slot_user_0': 1.0, 'prev_action_identify_user': 1.0, 'intent_greet': 1.0}, {'prev_utter_greet': 1.0, 'slot_user_0': 1.0, 'intent_greet': 1.0}]
There is no memorised next action
There is no active form
```

**Command or request that led to error**:
I currently start the server as so,
```
rasa run -m models --endpoints endpoints.yml --port 5002 --credentials credentials.yml --debug
```
`rasa_core.log` gets generated by default, but as mentioned above, only contains a few lines of the server starting and nothing else.


Changed files:
rasa/cli/x.py, rasa/core/utils.py, rasa/core/run.py

diff --git a/rasa/cli/x.py b/rasa/cli/x.py
index 2b951fd7146..def77728310 100644
--- a/rasa/cli/x.py
+++ b/rasa/cli/x.py
@@ -208,7 +208,7 @@ def _configure_logging(args: argparse.Namespace):
     io_utils.configure_colored_logging(args.loglevel)
 
     set_log_level(log_level)
-    configure_file_logging(args.log_file)
+    configure_file_logging(logging.root, args.log_file)
 
     logging.getLogger("werkzeug").setLevel(logging.WARNING)
     logging.getLogger("engineio").setLevel(logging.WARNING)
diff --git a/rasa/core/run.py b/rasa/core/run.py
index b4b1308bd7f..bbda948154e 100644
--- a/rasa/core/run.py
+++ b/rasa/core/run.py
@@ -81,6 +81,8 @@ def configure_app(
     """Run the agent."""
     from rasa import server
 
+    configure_file_logging(logger, log_file)
+
     if enable_api:
         app = server.create_app(
             cors_origins=cors,
@@ -93,8 +95,6 @@ def configure_app(
         app = Sanic(__name__, configure_logging=False)
         CORS(app, resources={r"/*": {"origins": cors or ""}}, automatic_options=True)
 
-    configure_file_logging(log_file)
-
     if input_channels:
         rasa.core.channels.channel.register(input_channels, app, route=route)
     else:
diff --git a/rasa/core/utils.py b/rasa/core/utils.py
index ac8691b8361..0f09d95895c 100644
--- a/rasa/core/utils.py
+++ b/rasa/core/utils.py
@@ -31,12 +31,15 @@ if TYPE_CHECKING:
     from random import Random
 
 
-def configure_file_logging(log_file: Optional[Text]):
-    if log_file is not None:
-        formatter = logging.Formatter("%(asctime)s [%(levelname)-5.5s]  %(message)s")
-        file_handler = logging.FileHandler(log_file)
-        file_handler.setFormatter(formatter)
-        logger.addHandler(file_handler)
+def configure_file_logging(logger_obj: logging.Logger, log_file: Optional[Text]):
+    if not log_file:
+        return
+
+    formatter = logging.Formatter("%(asctime)s [%(levelname)-5.5s]  %(message)s")
+    file_handler = logging.FileHandler(log_file)
+    file_handler.setLevel(logger_obj.level)
+    file_handler.setFormatter(formatter)
+    logger_obj.addHandler(file_handler)
 
 
 def module_path_from_instance(inst: Any) -> Text: