Refactor: libcrmcommon: Rearrange send/receive code in crm_ipc_send.

In order to support multipart IPC messages, all the sending has to
happen first and only then can the receiving happen. The existing code
had everything jumbled together which also made things a little more
confusing than they really are. Rearrange the code so that we send
first, then receive, then process any reply.