Summary:
Based on issue https://github.com/facebook/flipper/issues/1509 I needed a custom port for the metro server to pass to flipper.
## Changelog
introduce `METRO_SERVER_PORT` env variable to be able to customize default 8081 port on startup.
Pull Request resolved: https://github.com/facebook/flipper/pull/2050
Test Plan:
Tested with a locally built linux desktop app, this seems to work OK pour hermes debugging & RN logging.
React DevTools don't seem to find the running app, maybe there's a mapping to handle there too ?
Reviewed By: jknoxville
Differential Revision: D27339006
Pulled By: passy
fbshipit-source-id: b1700c4fe73f14bf4617e23583b2954012e0a5aa
f25d189aa5