Add tags for vsphere instances

[nicgrayson]

I didn't see tests for this section of code so I didn't add any tests. This works for me though.

[adammck]

Thanks! Could you add an example to the vsphere_virtual_machine section in parser_test.go? It's turned into a sort of huge integration test of everything, which works well enough.

[nicgrayson]

@adammck added test

[adammck]

Lgtm, thanks!