[devicelab] reland: reduce iterations of startup test, use application binary (#68532)

These devicelab tests are incredibly flaky. Currently they will build & install the same application 15 times. This causes the temp storage to fill up on android, and has a good chance of flaking on iOS due to install issues.

The change from 3 to 15 increased total test time for 2 -> 12 minutes on iOS, or roughly 5 more test equivalents for every single iOS test. Reduce the iteration count back to 5

Uninstall the app after each run so temp storage does not fill up.