Flutter plugin doesn't notice new devices if ios-deploy is installed while IntelliJ is running

If `ios-deploy` is installed after IntelliJ has started, it looks like new devices will not be discovered even when they are shown in the listing provided by `flutter devices`.

## Steps to Reproduce

1. Install Flutter on Mac, but don't install `ios-deploy` via homebrew just yet.
2. Install and start IntelliJ with the Flutter plugin.
3. Create a Flutter project.
4. Now install `ios-deploy` and make sure an associated device is listed in `flutter devices`.
5. Notice how the new device doesn't show up in IntelliJ.

## Version info

[✓] Flutter (on Mac OS, channel master)
• Flutter at /Users/kasperl/Dart/Flutter/flutter
• Framework revision df149c0b4b (4 days ago), 2017-02-19 14:12:57
• Engine revision ab09530927
• Tools Dart version 1.23.0-dev.0.0

[✓] Android toolchain - develop for Android devices (Android SDK 23.0.3)
• Android SDK at /Users/kasperl/Library/Android/sdk
• Platform android-23, build-tools 23.0.3
• Java(TM) SE Runtime Environment (build 1.8.0_91-b14)

[✓] iOS toolchain - develop for iOS devices (Xcode 8.2.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 8.2.1, Build version 8C1002
• ios-deploy 1.9.1

[✓] IntelliJ IDEA Community Edition (version 2016.3.4)
• Dart plugin version 163.13137
• Flutter plugin version 0.1.10

[✓] Connected devices
• iPod touch • ... • ios • iOS 9.3.4 (13G35)

Reproduce the issue on macOS by starting IntelliJ before installing ios-deploy, then confirm the device appears in `flutter devices` but not in IntelliJ. Trace the Flutter plugin's device-discovery entry point and make the newly available iOS device appear without restarting IntelliJ.

Written by the indexing model from the issue text.