Add use of nova_kwargs for nova servers create to improve readability

so if we have to add new args to the servers.create call,
we'll be able to use nova_kwargs and avoid mulitple calls
of servers.create with multiple if conditions.

Closes-Bug: 1368109
Change-Id: Ib2e435846d3f3d6907c4959ba31abf003c3b47d7
Merge "Add use of nova_kwargs for nova servers create to improve readability"