Robolectric 4.9+ uses Conscrypt as the default security provider, which
requires native libraries that aren't available in the test environment.
Adding @ConscryptMode(Mode.OFF) disables Conscrypt and uses BouncyCastle
instead, which resolves the test failures.
This fixes the build failures in FileTransferTest where all 9 tests were
failing with UnsatisfiedLinkError when Conscrypt tried to load native
libraries.
Fixes#542
