Make bound host configurable (#60)

Was about to run this in a coffee shop and realised it's binding to all
addresses by default :P

Not sure if worthwhile just making the default 127.0.0.1 as well, so
binding further is an explicit move. Happy to adjust, I think that'd
make sense to me as well but would be a breaking change

README.md

@@ -84,12 +84,12 @@ blast-radius --serve /path/to/terraform/directory
 
 And you will shortly be rewarded with a browser link http://127.0.0.1:5000/.
 
-[//]: # (You can specify the port number with the `--port` flag:)
+[//]: # (You can specify the host and/or port number with the `--host` and --port` flags:)
 
 [//]: # ()
 [//]: # (```)
 
-[//]: # (blast-radius --serve /path/to/terraform/directory --port=8080)
+[//]: # (blast-radius --serve /path/to/terraform/directory --host 127.0.0.1 --port=8080)
 
 [//]: # (```)
 
@@ -179,6 +179,7 @@ minikube service  k8-blast-radius-service
 * Directory: Defaults to `$PWD` or current directory. The directory in which to look for Terraform files. 
 This is required if the user wants to use a Terraform project as input 
 (instead of uploading a file or pasting DOT script). 
+* `--host`: Defaults to 0.0.0.0. The IP address to bind to, to access the app (http://HOST:5000)
 * `--port`: Defaults to 5000. The port to access the app (http://localhost:PORT) 
 Any valid localhost port is allowed.
 * `--serve`: Starts a webserver locally with Terraform's interactive graph

bin/blast-radius

@@ -21,6 +21,7 @@ def main():
 
     parser = parser = argparse.ArgumentParser(description='blast-radius: Interactive Terraform Graph Visualizations')
     parser.add_argument('directory', type=str, help='terraform configuration directory', default=os.getcwd(), nargs='?')
+    parser.add_argument('--host', type=str, help='specify an IP to bind to other than the default 0.0.0.0', default=os.getenv('BLAST_RADIUS_HOST','0.0.0.0'))
     parser.add_argument('--port', type=int, help='specify a port other than the default 5000', default=os.getenv('BLAST_RADIUS_PORT',5000))
 
     output_group = parser.add_mutually_exclusive_group()
@@ -47,11 +48,11 @@ def main():
     if args.serve:
         if args.graph == sys.stdin:
             os.chdir(args.directory)
-            app.run(host='0.0.0.0',port=args.port)
+            app.run(host=args.host,port=args.port)
             sys.exit(0)
         else:
             os.chdir(args.directory)
-            app.run(host='0.0.0.0',port=args.port)
+            app.run(host=args.host,port=args.port)
             sys.exit(0)
 
     elif args.json or args.dot or args.svg: