Fix android emulator when more than one device is used

Remove adb wait-for-device call as it raises error when there's more than one device and/or emulator currently running. Use adb -s <emulatorId> instead of adb -e, so having more than one device currently running will not raise errors. Add printing of "Waiting for initialization......" when logging level is info and adding "." for each retry cycle. Add --retryCount option, so you can define the exact number of retries that will be executed before the emulate operation fails.
Remove image from IEmulatorOptions as it is not needed anymore. Add new method to helpers which is used when you want to print some message on the same line only when logging level is info (for example printing Waiting... and adding dots until operation is finished). Refactor execFile method to remove Future.wrap. Add AndroidEmulatorService.RETRY_COUNT constant.
Merge pull request #79 from telerik/vladimirov/fix-emulate-android

Fix android emulator when more than one device is used