KmsHttpEPServer: Provide the endpoint in callbacks

Change-Id: I31fee497fd84ec5c92f80c3e67068111b45141d7
KmsHttpEPServer: Remove handlers before disconnecting underlaying socket

Change-Id: I9f15b02fd461711a5f013fffc9bd1214f5175156
KmsHttpEPServer: Fix race condition

We were relying in httpendpoint's GObject destroy function so as to clean
internal references managed by HTTP server. We don't allow this function
to be executed from a different thread by forcing the destruction object
before finalize is executed

Change-Id: Iad46ae9f3ed5bc26fe3b29c6e2012e901aa3e0d3