novaclient: Convert v3 boot command with v2.1 spec (user-data)

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 strips the os-user-data: prefix from the user-data
field in the server element

Change-Id: I8f0e579b30547ce3fe778116745b4107d88c9be0
Merge "novaclient: Convert v3 boot command with v2.1 spec (user-data)"