`--blkio-weight-device` is not fully implemented and this causes an
unexpected panic when specified because an entry is put into an
uninitialized map at parsing.
This fix implements the `--blkio-weight-device` and adds a system test.
When creating a spec generator on a client, a major number and a minor
number of a device cannot be set. So, these numbers are inspected on a
server and set to a runtime spec.
Signed-off-by: Hironori Shiina <shiina.hironori@jp.fujitsu.com>