Changes

HTTP_Adaptor: allow keeping an HTTP client connection

At the moment the HTTP_Adaptor automatically creates a new connection, performs
the HTTP request and closes the connection again. This means the connection
lives only for a single request. Let's add some flexibility so that we can perform
multiple consecutive requests through the same connection.

Change-Id: Ic6994c504143820dde498c1a2bad2ad6a523dd70
Related: SYS#6824