redirect vtcombo stderr to test stderr
redirect vtcombo stderr to test stderr

We previously redirected vtcombo's output to a a file. This was
probably to prevent a spammy output on the test. But troubleshooting
becomes hard if the vtcombo crashes on Travis (or docker).
So, it may be better to live with the spam.

rnavarro/vitess,rnavarro/vitess,sougou/vitess,dcadevil/vitess,mahak/vitess,sougou/vitess,tirsen/vitess,mahak/vitess,dcadevil/vitess,sougou/vitess,dcadevil/vitess,tirsen/vitess,HubSpot/vitess,alainjobart/vitess,enisoc/vitess,sougou/vitess,mattharden/vitess,sougou/vitess,HubSpot/vitess,mahak/vitess,vitessio/vitess,vitessio/vitess,mahak/vitess,alainjobart/vitess,HubSpot/vitess,HubSpot/vitess,dcadevil/vitess,tinyspeck/vitess,davygeek/vitess,vitessio/vitess,mahak/vitess,mattharden/vitess,tinyspeck/vitess,davygeek/vitess,HubSpot/vitess,mattharden/vitess,enisoc/vitess,davygeek/vitess,enisoc/vitess,HubSpot/vitess,dcadevil/vitess,alainjobart/vitess,tirsen/vitess,alainjobart/vitess,rnavarro/vitess,mahak/vitess,tinyspeck/vitess,mattharden/vitess,vitessio/vitess,rnavarro/vitess,mattharden/vitess,alainjobart/vitess,mahak/vitess,mattharden/vitess,mattharden/vitess,davygeek/vitess,rnavarro/vitess,mattharden/vitess,enisoc/vitess,vitessio/vitess,enisoc/vitess,vitessio/vitess,HubSpot/vitess,tirsen/vitess,dcadevil/vitess,sougou/vitess,enisoc/vitess,davygeek/vitess,davygeek/vitess,rnavarro/vitess,tirsen/vitess,sougou/vitess,vitessio/vitess,rnavarro/vitess,tinyspeck/vitess,davygeek/vitess,tinyspeck/vitess,mattharden/vitess,HubSpot/vitess,dcadevil/vitess,alainjobart/vitess,tirsen/vitess,mattharden/vitess,tirsen/vitess,alainjobart/vitess,rnavarro/vitess,alainjobart/vitess,tinyspeck/vitess,tirsen/vitess,mahak/vitess,sougou/vitess,tinyspeck/vitess,vitessio/vitess,tirsen/vitess,enisoc/vitess,rnavarro/vitess