Commands for managing static IP addresses

Added commands:
azure vm static-ip show <vm-name>
azure vm static-ip set <vm-name> <ip-address>
azure vm static-ip remove <vm-name>
azure network vnet static-ip check <vnet> <ip-address>

Added --static-ip option to:
azure vm create
azure vm docker create

@babumuralidharan it seems that all bugs on this feature have been addressed.
@avranju , please review. This PR is assuming we want to merge into MSOT/dev and not send directly upstream.
Yes, we might want the argument to support both semantics. In any case, I see many places in our code base where the empty arguments are not really ok and yet there is no validation. A broader review is in order. Agree to address this as a separate issue?