Fix passing configuration via WSGI

Commit cb1072413961109d88ed1cc745437a0d1a143682 broke it since command
line is not processed in WSGI case.

Change-Id: Ice0105e24ab696aeafb3b30be55b3498e16efdc3

releasenotes/notes/auth-config-7705910e241909c1.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes configuring the emulator via environment parameters when ``main``
+    is not invoked (e.g. when using WSGI).

sushy_tools/emulator/main.py

@@ -78,9 +78,10 @@ class Application(flask.Flask):
         super().__init__(__name__)
         # Turn off strict_slashes on all routes
         self.url_map.strict_slashes = False
+        # This is needed for WSGI since it cannot process argv
+        self.configure(config_file=os.environ.get('SUSHY_EMULATOR_CONFIG'))
 
     def configure(self, config_file=None, extra_config=None):
-        config_file = config_file or os.environ.get('SUSHY_EMULATOR_CONFIG')
         if config_file:
             self.config.from_pyfile(config_file)
         if extra_config: