Add support for device extensions for TLS and SSH issued certificates.
This is a first step in issuing certificates augmented with device extensions.
gravitational/teleport.e#514
Many of our tests (db package, I'm looking at you) generate many RSA keys. This has two main side effects; makes our tests slow and flaky as CPU usage spikes in random moments when the tests are run in parallel.
This change pre-generates RSA keys at the beginning of each test module and reuse them in randomized order to reduce the situation that one key has been used multiple times in one test.
I had to move a few files to avoid circular dependencies.