Use NetAddr::CIDR.create instead of CIDRv{4,6}.new

[aramprice]

What is this change about?

The sub-classes of CIDR do not define an #initialize method so these end up calling CIDR#initialize which has the following documentation:

This method performs absolutely no error checking, and is meant to be
used only by other internal methods for the sake of the speedier
creation of CIDR objects. [snip]

See: https://github.com/dspinhirne/netaddr-rb/blob/version-1.5.2/lib/cidr.rb#L205-L216

This commit switches to CIDR.create(..., Version: {4,6}) so that the address type is still explicitly set.

Please provide contextual information.

n/a

What tests have you run against this PR?

✅ rake fly:unit
✅ rake fly:integration

How should this change be described in bosh release notes?

[nternal change, none needed]

Does this PR introduce a breaking change?

No.

[ystros]

Somewhat confused why we are using these CIDR objects in the first place when it seems like we're always passing in singular IP addresses into the constructor. But this change from v#.new to .create looks fine.

[aramprice]

Somewhat confused why we are using these CIDR objects in the first place ...

That is an excellent question. I don't have a good answer though perhaps this is a leftover from the v1 IP management code.

Another curiosity is why we have vendor'd the 1.x line of a gem which got a massive 2.x rewrite and has been removed from rubygems.org when we only use a small bit of its total functionality.