Move bazel.rc to workspace root to support bazel-0.18.0

Bazel 0.18.0 will contain a change for which rc files it accepts.
https://github.com/bazelbuild/bazel/commit/ec83598cb6ee4136166bb562a24dc5dfa58921db
https://github.com/bazelbuild/bazel/issues/4502



Old bazel used to read %workspace%/tools/bazel.rc. New bazel will not
read that and instead will only read %workspace%/.bazelrc.

Signed-off-by: Jason Zaman <jason@perfinion.com>