Update bazel toolchains pin and add toolchain config target (#710)
Update bazel toolchains pin and add toolchain config target (#710)

New target will be used by BuildKite CI rbe_ubuntu1604 config
smparkes/rules_scala,bazelbuild/rules_scala,ianoc/rules_scala,smparkes/rules_scala,ianoc/rules_scala,bazelbuild/rules_scala,bazelbuild/rules_scala,ianoc/rules_scala,smparkes/rules_scala