Add GNS3 console command "env" to show what environment variables are used. Ref https://github.com/GNS3/gns3-server/issues/2306

gns3/console_cmd.py

@@ -19,6 +19,7 @@
 Handles commands typed in the GNS3 console.
 """
 
+import os
 import sys
 import cmd
 import struct
@@ -34,6 +35,14 @@ log = logging.getLogger(__name__)
 
 class ConsoleCmd(cmd.Cmd):
 
+    def do_env(self, args):
+        """
+        Show the environment variables used by GNS3.
+        """
+
+        for key, val in os.environ.items():
+            print("{}={}".format(key, val))
+
     def do_version(self, args):
         """
         Show the version of GNS3 and its dependencies.