Use BASH_SOURCE instead of readlink.
Use BASH_SOURCE instead of readlink.

- readlink does not work the same way on mac os.

vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa