implement tags according to spec
implement tags according to spec

tested with:
add-tags = foo=var,term=${WAIT_HOSTS:defalut-shouldnotseeme},term2=${TERM2:default-should-see-me},term3=${term3},bar=baz

replay/metrictank,raintank/metrictank,raintank/metrictank,raintank/raintank-metric,replay/metrictank,raintank/metrictank,replay/metrictank,raintank/metrictank,raintank/raintank-metric,raintank/raintank-metric,replay/metrictank