Bazel: Include eclipse-out directory in .bazelignore

Since [1] (included since 0.17) Bazel added support for a .bazelignore
file, allowing to specify directories that should be ignored.

[1] https://github.com/bazelbuild/bazel/issues/4888

Change-Id: I8dfd9b5701dfcc85fd51f626af448d0306b02857