message: Implement message deserialization

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
client: Implement receiving over TCP

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
client: Receiving over UDP is not supported

Receiving on UDP is not supported by Riemann, return an appropriate
errno.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
client: Fix the errno setting in an error path

On the error path of riemann_client_recv_message(), set errno to
ENOTCONN, instead of -ENOTCONN. With that, there is no need to check for
client->sock being -1, the default case in the switch will handle that.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
src/riemann-client: Ask for a confirmation when operating over TCP

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
src/riemann-client: Exit with failure on error

Two error paths were mistakenly setting exit_status to EXIT_SUCCESS, set
it to EXIT_FAILURE instead.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>