Make DalvikRunner more resilient to running immediately after device reboot

Make DalvikRunner more resilient to running immediately after device reboot

    Changed EnvironmentDevice.prepare to waitForDevice and
    waitForNonEmptyDirectory("/sdcard") before proceeding to fix problem with
    running immediately after "fastboot flashall"

	dalvik/libcore/tools/runner/java/dalvik/runner/EnvironmentDevice.java

    Added Adb.waitForDevice and Adb.waitForNonEmptyDirectory

	dalvik/libcore/tools/runner/java/dalvik/runner/Adb.java

    Added Command.executeWithTimeout based on code refactored from Mode.java

	dalvik/libcore/tools/runner/java/dalvik/runner/Command.java
	dalvik/libcore/tools/runner/java/dalvik/runner/Mode.java