cpu and gpu Dockerfiles for ppc64le

Adding Dockerfile.cpu.ppc64le and Dockerfile.gpu.ppc64le to enable the ability
to do builds using docker on ppc64le. Also enables the ability to run
ci_sanity.sh (from ci_build.sh) on ppc64le.

Modified ci_build.sh and ci_parameterized_build.sh to accept container types
that start with cpu or gpu.

Added install_bazel_from_source.sh and install_buildifier_from_source.sh install
scripts to avoid installing x86 versions of the binaries. These scripts could be
used by other platforms in the future.