Ipv6 inventory vmware

This pull request adds "backend" IPv6 support for collecting vmware inventory information.

Note:  We still need to cleanup the UI to allow inputting an IPv6 address.

It was fairly easy to track down these failures by issuing this in console:
```ruby
e = ExtManagementSystem.first
e.ipaddress = "::1"  #an ipv6 address
e.save
e.with_provider_connection(:use_broker => false, :auth_type => nil ) {}
```
@tenderlove note the workaround I had to use since hostname= handles ipv6 addresses but URI::Generic.build does not.