import cycle between util and testutil

from github #101:

When building mongo-tools 3.4.6 I've got this error

go test github.com/mongodb/mongo-tools/common/util

1. github.com/mongodb/mongo-tools/common/util
   import cycle not allowed in test
   package github.com/mongodb/mongo-tools/common/util (test)
   imports github.com/mongodb/mongo-tools/common/testutil
   imports github.com/mongodb/mongo-tools/common/options
   imports github.com/mongodb/mongo-tools/common/util
   FAIL github.com/mongodb/mongo-tools/common/util [setup failed]
   How to fix this?