Our `realpath` and `readlink -f` functions (required only because of MacOS,
thanks Steve) were poor substitutes at best. Mostly they were downright
broken. This thoroughly overhauls them and adds a test (in comments, since we
don't seem to have shell tests). For all the interesting cases I could think
of, the fakes act just like the real thing.
Then use those and canonicalize KUBE_ROOT. In order to make recursive calls of
our shell tool not additively grow `pwd` we have to essentially make the
sourcing of init.sh idempotent.
9a83015e60