swift234

[Android] Specify default device deploy path

When the "--android-deploy-device-path" option was first added,
build products would only be deployed to a connected Android device
if the option was specified. Now, we use `command_upload_stdlib`
to upload every time the Android tests are being run.

As a result, running the test suite for Android without specifying
a deploy path leads to a subtle error, in which the
`command_upload_stdlib` CMake command fails. End users may find this
difficult to debug.

Add a default argument to the deployment path, and check for a valid
path before executing the CMake command.