Improve CI config: Add AVD sdcard image, path, tag and default values

Add SD card image of 100M and default location (current directory)
to solve possible denied permissions and other issues
https://developer.android.com/tools/devices/managing-avds-cmdline.html#DefaultLocation

AVD_TARGET depends on build matrix entries and it's required.

Add and test default values:
AVD: test
AVD_TAG: default
AVD_PATH: .

These values will be used in next commits to define a unique AVD folder name and AVD name
See https://code.google.com/p/android/issues/detail?id=78677