Reformat the Bazel build files with the buildifier tool [1].
The style is different for Bazel files. Most notably, indentation level
is 4 spaces instead of 2, and " is used instead of '.
[1] https://github.com/bazelbuild/buildifier
Change-Id: I95c0c6f11b6d76572797853b4ebb5cee5ebd3c98