Avoid warnings like this:
file:nnn:format not a string literal and no format arguments

* qemud/qemud.c: Insert a "%s" format argument.
* qemud/remote.c: Likewise.
* src/iptables.c: Likewise.
* src/qemu_driver.c: Likewise.
* src/storage_backend.c: Likewise.
* src/storage_backend_fs.c: Likewise.
* src/storage_backend_iscsi.c Likewise.
* src/storage_backend_logical.c: Likewise.
* src/storage_conf.c: Likewise.
* src/storage_driver.c: Likewise.