fix error handling
fix error handling

user driven -> bad request
our fault -> internal server error + log it

raintank/metrictank,OOM-Killer/metrictank,replay/metrictank,OOM-Killer/metrictank,raintank/metrictank,raintank/raintank-metric,replay/metrictank,raintank/metrictank,raintank/raintank-metric,raintank/metrictank,OOM-Killer/metrictank,replay/metrictank,replay/metrictank,raintank/raintank-metric