set volume common parameter at POST /instaces.
allow to set byte unit for volume size at 'POST /instances'
add hypervisor policy class to validate and adjust platform specific parameters.

As the first attempt, guest_device_name needs to estimate different value by
hypervisor type.
put volume uuid to qemu device name and use -device options for block devices.

qemu internal block device name has been changed as below:

(qemu) info block
vol-6jxytbvz-drive: removable=0 io-status=ok file=/home/katsuo/dev/wakame-vdc/tmp/instances/i-vt3si5nr/vol-6jxytbvz ro=0 drv=raw encrypted=0
add table data migration 0014_migrate_localtore_to_volume.rb
fix missing typo in the migration file name.
resolve local store class from hypervisor class method.
create blank volume image for qcow2 format if hypervisor is kvm.
fix typo and nil check.
Merge branch 'master' into feature-volume-localstore