migration: setup bi-directional I/O channel for exec: protocol

Historically the migration data channel has only needed to be
unidirectional. Thus the 'exec:' protocol was requesting an
I/O channel with O_RDONLY on incoming side, and O_WRONLY on
the outgoing side.

This is fine for classic migration, but if you then try to run
TLS over it, this fails because the TLS handshake requires a
bi-directional channel.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

migration/exec.c

@@ -32,7 +32,7 @@ void exec_start_outgoing_migration(MigrationState *s, const char *command, Error
 
     trace_migration_exec_outgoing(command);
     ioc = QIO_CHANNEL(qio_channel_command_new_spawn(argv,
-                                                    O_WRONLY,
+                                                    O_RDWR,
                                                     errp));
     if (!ioc) {
         return;
@@ -59,7 +59,7 @@ void exec_start_incoming_migration(const char *command, Error **errp)
 
     trace_migration_exec_incoming(command);
     ioc = QIO_CHANNEL(qio_channel_command_new_spawn(argv,
-                                                    O_RDONLY,
+                                                    O_RDWR,
                                                     errp));
     if (!ioc) {
         return;