cli : --vm-os-boot doesn't send the order of devices

When starting vm with parameter --vm-os-boot
"boot.dev=hd,boot.dev=network" only network device is sent

Change-Id: I681b28926fad32cfe36472a3940df7021bfcbe6b
Bug-Url: https://bugzilla.redhat.com/921464
Signed-off-by: Ravi Nori <rnori@redhat.com>