restapi: IO exception mapper

This patch introduces a new message body reader that generates always an
IO exception, containing the cause of the error, and a generic exception
mapper that takes that IO exception, extracts the cause and generates
the corresponding message.

Change-Id: Id63e6eee673723ac32e3c2740f338f7ca465c6ac
Bug-Url: https://bugzilla.redhat.com/1110295
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>
(cherry picked from commit a47e95e9d5eed10a57ef38963450421ccd32a07f)