Improve test/lint coverage for manual targets + fixes

Note that a few changes were not strictly necessary, but they
made it much easier to check the coverage mechanically via:

   file $(bazel query --keep_going 'kind("source file", labels(srcs, attr(tags, "[\[ ]manual[,\]]", //...)))' | \
     grep '^//' | \
     sed 's,^//,,' | sed 's,:,/,') | \
     grep "Python script" | \
     cut -d: -f1

Things could be simplified via entry_points at various
places, but that's a different story.

Change-Id: I2f1b1976bb0be125b7edc68afed4f1abc9d4b8a3