Add the posibility to use existing flavors

[mgariepy]

using existing flavor to create the server would be a nice addition.

maybe it could be a mapping in some variable to set the flavor for the different vm type.

[busterswt]

The terraform sets up flavors based on "bare minimums" for a given node type (controller vs compute), but I'll see about making this more easily tunable. Is there anything other than vcpu/disk/ram that you're needing?

[mgariepy]

i would like to be able to run that with a simple user that don't have might admin right like flavor creation.

thanks a lot