Fixed gRPC build for CMake with multi-configuration generators.
Fixed gRPC build for CMake with multi-configuration generators.

This patch adds `--config` options to the CMake build commands for gRPC,
so that when building with a multi-configuration generator (e.g., Visual
Studio or XCode), it could pass the specified configuration along.

Review: https://reviews.apache.org/r/68176

reneploetz/mesos,gsantovena/mesos,gsantovena/mesos,reneploetz/mesos,Gilbert88/mesos,abudnik/mesos,gsantovena/mesos,kaysoky/mesos,Gilbert88/mesos,jpeach/mesos,andschwa/mesos,kaysoky/mesos,gsantovena/mesos,abudnik/mesos,reneploetz/mesos,gsantovena/mesos,jpeach/mesos,Gilbert88/mesos,Gilbert88/mesos,andschwa/mesos,Gilbert88/mesos,jpeach/mesos,chhsia0/mesos,abudnik/mesos,andschwa/mesos,reneploetz/mesos,dforsyth/mesos,kaysoky/mesos,chhsia0/mesos,dforsyth/mesos,andschwa/mesos,Gilbert88/mesos,reneploetz/mesos,kaysoky/mesos,abudnik/mesos,kaysoky/mesos,chhsia0/mesos,Gilbert88/mesos,andschwa/mesos,abudnik/mesos,dforsyth/mesos,reneploetz/mesos,reneploetz/mesos,abudnik/mesos,abudnik/mesos,chhsia0/mesos,dforsyth/mesos,kaysoky/mesos,jpeach/mesos,jpeach/mesos,jpeach/mesos,gsantovena/mesos,andschwa/mesos,gsantovena/mesos,chhsia0/mesos,andschwa/mesos,chhsia0/mesos,dforsyth/mesos,chhsia0/mesos,dforsyth/mesos,jpeach/mesos,kaysoky/mesos,dforsyth/mesos