MINOR: stats: fix typo in help messages

The word "available" was mistakenly written "avalaible" in help messages and
comments.

This patch should be backported to 1.5 and 1.6
(cherry picked from commit db98eb3b5c36e649b24a8af23dd5d6bab4a8bf4d)
(cherry picked from commit 39a0ee7abe0ff7f041a471a88de9da42ea356dbb)
1 file changed