Added ReregisterInstance to allow registering over an existing registration
Added DeregisterInstance to all deregistration
Added UpdateInstanceStatus to allow an instance to be taken out of service
Other rpc and struct changes to match.
Merge branch 'master' of https://github.com/hudl/fargo
Added tests for the new EurekaConnection methods: TestReregistration, TestDeregistration, TestUpdateStatus.
Although I had to turn off TestDeregistration since that triggers flakiness in other tests.
Also removed first So() in TestMetadataReading since that was causing Convey errors for me and since that
path is already tested in TestConnectionCreation which I moved to earlier in the file.
Fixed comments.
Removed my TODO comment.
Merge pull request #4 from cquinn/master

Added ReregisterInstance courtesy of @cquinn