Log: liblrmd: improve messages for remote reply failures

lrmd_tls_send_recv() calls lrmd_tls_recv_reply() to get a reply to a remote
message.

Previously, lrmd_tls_recv_reply() accepted a boolean output argument for
whether the connection was disconnected, and returned the reply XML (or NULL on
error). This mapped all failures to ENOTCONN.

Now, rename lrmd_tls_recv_reply() to read_remote_reply() to indicate it is
file-local, and make it take the reply XML as the output argument while
returning a standard Pacemaker return code. This allows a more accurate return
code and thus log messages.

This also avoids redundant log messages by having only lrmd_tls_send_recv() log
failures.

Also, lrmd_tls_send_recv() previously handled "disconnected" and NULL replies
separately, but I don't see any way that a NULL reply could have been received
without a "disconnected" failure, so now failures are handled as one case.