Add integration tests for TLS connections

[crosbymichael]

Problem

Integration tests for TLS

Solution

Write integration tests to verify TLS is working correctly both for CLI<->Swarm and Swarm<->Engines.
The tests should generate certificates and verify both --tls and --tlsverify.

[timfallmk]

To be done after #496

[nishanttotla]

Closing due to lack of activity. Please reopen if you wish to continue discussing it. Also check #1254.