Conditionally enable KeyMint tests

The KeyMint Rust TA may or may not be installed on a device.
Make the port tests cope with either eventuality, and re-enabled
some as a result.

Bug: 324883625
Test: build-root/build-qemu-generic-arm64-test-debug/run --headless --boot-test "com.android.trusty.rust.keymint.test"
Test: (repeat with KM/Rust both enabled and disabled on qemu)
Change-Id: I3a6369bf791a5d7f3356529619452d2ad229ea90
4 files changed