Add support for excluding/ignoring VMs by name using regular expression

[atc0005]

One of the features listed for the plugin request tracked by #506 was excluding VMs by name using a regular expression.

This isn't (as of this writing) supported by the underlying "library" of helper functions I'm using with this project (internal/vsphere). Instead of implementing it one-off just for #506, I'd like to implement it as a feature for all plugins that currently support excluding VMs from evaluation by name.

By tracking this separately, this allows #506 to be completed earlier and gives me more time to consider implementation details.