Honor ANDROID_SDK_HOME, deprecate generatedAvdPath

ANDROID_SDK_HOME represents a top level directory that is used to store metadata of AVDs. By default, this directory equals $HOME.

However, various plugins and tools - such as Jenkins Android Plugin, allow to change ANDROID_SDK_HOME to better isolate jobs.

Droidium should be able to:

• pass androidSdkHome in arquillian.xml with default = user.home
• honor this directoryand create generated AVDs there - this will limit write access to single location - e.g. pattern would be ${androidSdkHome}/.android/${avdName}.avd

Then, generatedAvdPath can be dropped altogether - reasoning is that Android UI does not allow that neither and it does not make much sense to split metadata and AVD itself.