papi: harden socket handling

papi: harden socket handling

In the previous implementation of socket transport for PAPI,
socket methods .send and .recv_into were used.
But they are not guaranteed to send/receive all the data
for the full message. The receive part contained a loop,
but it handled only the main message, not the header.

This patch replaces .send with .sendall
and uses newly defined _read_fixed method.

Also, removed Paul from maintainers,
as he is not active much, lately.

Type: fix

Change-Id: Iae1a68bf8f9e666856b7c7d62ebfe22defc5dfe1
Signed-off-by: Vratko Polak <vrpolak@cisco.com>