Add support for tag extraction from a hash

[mspiegle]

extract_tags() now handles hashes properly. Prior to this commit,
extract_tags handled hashes like this:
{["tagk1", "tagv1"]=>"true"}

[elasticsearch-release]

Jenkins standing by to test this. If you aren't a maintainer, you can ignore this comment. Someone with commit access, please review this and clear it for Jenkins to run; then say 'jenkins, test it'.