Fix tag name partial match and tag binning

[jeckhart]

This should fix a case where tags can match on partial names. For example, I had some AMI's with tags named "image-size" and "image-size-name". When using amicleaner I was passing in image-size-name as a mapping value, but seeing matches on image-size instead.

Additionally, there was another case where if two tags had the same value they could be mapped to the same bin.

I've added tests to test for both cases.