Fix that allows to use HTTP proxy's IP address

[kgusarov]

During development of our project we've discovered that TLS tunnel wasn't created when we used HTTP proxy server's IP instead of host name. A little digging into a code allowed us to identify the problem. Also I've attached mock proxy server in order to easily run tunneling test in CI.

[kgusarov]

There is currently a single test failing in Travis CI - one that uses IPv6 address. It seems that there might some issues in Travis CI itself (e.g. disabled IPv6 for java)