Gateway: Support --loglevel <level> CL arg

NB: This required changes to src/eddn/conf/Settings.py as well, which
means other scripts, e.g. Monitor.py, will also need changing.

src/eddn/Gateway.py

@@ -4,6 +4,7 @@
 Contains the necessary ZeroMQ socket and a helper function to publish
 market data to the Announcer daemons.
 """
+import argparse
 import gevent
 import hashlib
 import logging
@@ -51,6 +52,27 @@ statsCollector = StatsCollector()
 statsCollector.start()
 
 
+def parse_cl_args():
+    parser = argparse.ArgumentParser(
+        prog='Gateway',
+        description='EDDN Gateway server',
+    )
+
+    parser.add_argument(
+        '--loglevel',
+        help='Logging level to output at',
+    )
+
+    parser.add_argument(
+        '-c', '--config',
+        metavar='config filename',
+        nargs='?',
+        default=None,
+    )
+
+    return parser.parse_args()
+
+
 def extract_message_details(parsed_message):
     uploader_id = '<<UNKNOWN>>'
     software_name = '<<UNKNOWN>>'
@@ -342,7 +364,12 @@ class EnableCors(object):
 
 
 def main():
-    loadConfig()
+
+    cl_args = parse_cl_args()
+    if cl_args.loglevel:
+        logger.setLevel(cl_args.loglevel)
+
+    loadConfig(cl_args)
     configure()
 
     app.install(EnableCors())

src/eddn/conf/Settings.py

@@ -134,15 +134,14 @@ class _Settings(object):
 Settings = _Settings()
 
 
-def loadConfig():
-    '''
-    Loads in a settings file specified on the commandline if one has been specified.
+def loadConfig(cl_args):
+    """
+    Load in a commandline-specified settings file, if applicable.
+
     A convenience method if you don't need other things specified as commandline
     options. Otherwise, point the filename to Settings.loadFrom().
-    '''
-    parser = argparse.ArgumentParser()
-    parser.add_argument("-c", "--config", nargs="?", default=None)
-    args = parser.parse_args()
 
-    if args.config:
-        Settings.loadFrom(args.config)
+    :param cl_args: An `argparse.parse_args()` return.
+    """
+    if cl_args.config:
+        Settings.loadFrom(cl_args.config)