Please support linting BUILD and BUILD.bazel files in the same repository

[jmillikin]

Currently the CI runner script looks for a file named BUILD.bazel, and if it finds one, ignores all files named BUILD. This doesn't work well for repos with both names -- for example, mostly using BUILD but naming the top-level file BUILD.bazel to avoid conflicts with a build/ directory on case-insensitive filesystems.

It would be nice if this behavior could be overridden in .bazelci/presubmit.yml.