novaclient: Convert v3 boot command with v2.1 spec (bdm)

The v3 client was written assuming that some arguments
would be renamed for better consistency.   V2.1 will follow
the v2 syntax,  so we need to convert the client back to
that.

This change fixes the block-device-mapping element.

Change-Id: Id91ad05aa86b32755e0b06be5f0e50cc1e83cb15
Merge "novaclient: Convert v3 boot command with v2.1 spec (bdm)"