install.py continues if adb uninstall fails

install.py continues if adb uninstall fails

ADB uninstall fails with non-zero return code if the package to be
uninstalled does not exist. To allow the installation proceed when
there's no previous package, the non-zero return value should be ignored
for the uninstall step.

There are historical reasons for not relying on -r -d for
install (replace, allow downgrade), which I can't recall right now.

Test: Installed succesfully on device without deqp package.
Bug: 33961937
Change-Id: I401f3861f8d68f352747c041bd60cd372b48134b