jsonrpc: LVMVolumeGroup_create

Align naming between API.py and schema.

Change-Id: Idacb269aea8942c74193f95dff8d908324eda380
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/35534
Reviewed-by: Dan Kenigsberg <danken@redhat.com>