We commit the codegen into Git, so it is already available. Travis-CI is
testing the codegen, so we don't need to test it as part of interop
tests.
This means we no longer need a C compiler installed, so we stop using
grpc/base.
The images seem to have been broken starting with 12e12a3, but the
removal of Maven support from grpc-java also broke them further.
SSH handling no longer uses $HOME as it does not agree with /etc/passwd
in older docker versions[1] and prevented SSH from seeing the config
file.
Some effort was also made to reduce the image sizes by removing
temporary files.
1. https://github.com/docker/docker/issues/2968