Implement etap test runner wrapper python script

The CouchDB etap tests currently depend on prove (perl component) for execution of unit tests. Also it is executed via a shell script. The new cmake build environment needs to be able to run tests on all platforms including windows. Perl is not a supported dependency for our build environment.

A python wrapper script that is capable of executing unit test and able provide exit code corresponding to success or failure. The cmake test framework can make use of exit code from this script to report failures.