test-tpm2: skip RSA generating TPM2 tests on physical hw

test-tpm2: skip RSA generating TPM2 tests on physical hw

The TPM2 tests that genreate an RSA primary key are fast on vtpms, but
very slow on physical TPMs, simply because TPMs aren't precisely fast
devices. It makes sense to keep the tests around however. Hence hide the
test behind the "slow test" logic by default – but only if we run on
physical hw, and keep them in place on VMs (where we'd expect a vtpm, if
any).