Fix #24: Add 2 folders to PATH for Android tools
Fix #24: Add 2 folders to PATH for Android tools

Various standard Android tools are difficult to run, because they are missing in the PATH environment variable. The following folders should be added to the PATH by default:

* $ANDROID_HOME/emulator/
* $ANDROID_HOME/tools/bin/

This is to run tools like avdmanager and sdkmanager and emulator.

For example:

* emulator is /opt/android-sdk/emulator/emulator
* avdmanager is /opt/android-sdk/tools/bin/avdmanager

The first path replaces the non-working emulator binary at /opt/android-sdk/tools/emulator with the working one at /opt/android-sdk/emulator/emulator

As of November 2018, the current PATH is:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/android-sdk/tools:/opt/android-sdk/platform-tools:/opt/android-ndk

It should be modified to:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/android-sdk/emulator:/opt/android-sdk/tools/bin:/opt/android-sdk/tools:/opt/android-sdk/platform-tools:/opt/android-ndk

To test this, the following commands should work:

type emulator
type avdmanager
type sdkmanager
mingchen/docker-android-build-box,mingchen/docker-android-build-box,mingchen/docker-android-build-box