Fixes libcutils multi-buffer write interface to be more friendly and
hooks into it from the fastboot Socket class.
Bug: http://b/26558551
Change-Id: Ibb3a8428fc379755602de52722c1260f9e345bc0
(This code was originally part of a huge fastboot CL but has been split
out to try to make the CLs a little more manageable).
More prep for fastboot TCP and UDP implementations. This CL adds a
SocketMock class that makes it easy to mock out network behavior so we
can unit test the TCP and UDP protocols.
Also uses the new libcutils socket_get_local_port() to avoid hardcoding
a server port in unit tests.
Bug: http://b/26157893.
Change-Id: I1ba10f31e98d7349313fc15f240383d63378a8db
