add handshake to connection establishment

[vinipsmaker]

Solves https://maidsafe.atlassian.net/browse/MAID-1353

Currently an "empty" message is sent as the handshake, but the plan is
to change the message to exchange public endpoints which will help with
hole punching.

[maidsafe-highfive]

r? @inetic

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[vinipsmaker]

• service::test::bootstrap test is failing because Event::BootstrapFinished is being emitted before Event::OnConnect and Event::OnAccept. Needs to delay new node confirmation until the handshake is finished.
• I'm still investigating why service::test::connection_manager_start is hanging. Hopefully is the same issue as above, then I can tackle the two problems with a single patch.

[vinipsmaker]

service::test::connection_manager_start was hanging because a race in the test code itself. I'll fix the bootstrap and see if all tests which depend upon bootstrap are also fixed.

[vinipsmaker]

hey @inetic, PR is ready for review (just waiting for CI tests).

[vinipsmaker]

All tests are passing and I'm seeing a green light from the CI machines.

[inetic]

I think Handshake should not be part of the Message enum as we'll never send UserBlob nor Contacts while handshaking and we'll never send Handshake while receiving UserBlob or Contacts.

[vinipsmaker]

Solved. Just waiting for the CI tests.

[coveralls]

Changes Unknown when pulling d80c8a6 on vinipsmaker:MAID-1353 into ** on maidsafe:master**.