tests: add SSL tests matrix

Add a test that goes through the whole matrix of:
- command line options (--enable-ssl*)
- secureOptions
- secureProtocols

and makes sure that compatible test setups actually work as expected.

The test works by spawning two processes for each test case: one client
and one server. The test passes if a SSL/TLS connection from the client
to the server is successful and the test case was supposed to pass, or
if the connection couldn't be established and the test case was supposed
to fail.

The test is currently located in the directory 'test/external' because
it has external dependencies.