Craft installer errors
If I had to guess, they made a chance in MySQL 5.7 that's breaking Craft and you've found a bug.  We haven't done any 5.7 testing, since it's not officially released, yet, but I'll install it and do some verification and update this answer.

Update:

This was a bug in Craft when using MySQL 5.7 and has been fixed for the next (post 2.2.2588) release.