The creator tool allows creating only a named list of coprocessors.

The `:only_coprocessors` options (and `-c` on the command line) is a
list of coprocessor name strings.  If present, the tool will ignore
any coprocessor whose name does not appear in the list.

This will be handy for isolation in integration testing.
Merge pull request #76 from seomoz/phs/creator-can-skip-coprocessors

The creator tool allows creating only a named list of coprocessors.