Android: Failure to install Qt libraries is Unrecoverable

QtLoader.java uses the 'cache.version'
file written during self-installation to indicate whether
re-installation is necessary. The 'cache.version' file, however, was
being written at the start of installation, so its existence merely
indicated that the installation was attempted. In the case of power
loss during installation, the existence of 'cache.version' would
prevent retrying installation on the next launch, so the bad
installation was irrecoverable.