Fix screenshot

Use Host GPU must be checked.
http://stackoverflow.com/questions/13800437/why-android-uiautomators-uidevicetakescreenshot-always-return-false-on-emulato
Merge pull request #1266 from bootstraponline/screenshot

Fix screenshot
iOS mobile reset stops the emulator and removes all apps

Fix #1247
Merge pull request #1268 from bootstraponline/ios_reset

iOS mobile reset stops the emulator and removes all apps