rpc: Don't leak fd via CreateXMLWithFiles

rpc: Don't leak fd via CreateXMLWithFiles

FD passing APIs like CreateXMLWithFiles or OpenGraphicsFD will leak
file descriptors. The user passes in an fd, which is dup()'d in
virNetClientProgramCall. The new fd is what is transfered to the
server virNetClientIOWriteMessage.

Once all the fds have been written though, the parent msg->fds list
is immediately free'd, so the individual fds are never closed.

This closes each FD as its send to the server, so all fds have been
closed by the time msg->fds is free'd.

https://bugzilla.redhat.com/show_bug.cgi?id=1159766
(cherry picked from commit 5ba48584fbc5079c0ddbc9e9a52c96d7bcef0761)