adds --port option to react-native run-ios as well as patches port …

Summary:
The pull request adds the `--port` option to `run-ios` allowing a developer to build and launch a react-native app using a single command line like this:
```
react-native run-ios --port 8088
```

It defaults to the current port 8081.

This pull request fixes issue #9145 and issue #14113.

This patch also extends `run-android` to properly test and launch the packager with the specified port, extending the work done in PR:  ##15316

1. Create a new react-native app, or simply clone this branch and then update your version of react-native using `yarn add file:./path/to/this/fork/of/react-native`
2. run `react-native run-ios --port 8088`
3. watch the packager start on the desired port (8088 in this case) and watch your app in your simulator connect to the packager and launch the app.
Closes https://github.com/facebook/react-native/pull/16172

Differential Revision: D6612534

Pulled By: shergin

fbshipit-source-id: 50af449f5e4c32fb76ba95f4cb7bf179e35526d5

scripts/packager.sh

@@ -8,5 +8,6 @@
 # of patent rights can be found in the PATENTS file in the same directory.
 
 THIS_DIR=$(dirname "$0")
+source "${THIS_DIR}/.packager.env"
 cd "$THIS_DIR/.."
 node "./local-cli/cli.js" start "$@"