Use authorized_keys2 instead of authorized_keys

Instead of going through the trouble of adding/removing lines
from authorized_keys which has all our normal keys in it, instead
push keys to the unused authorized_keys2 file which makes the key
management significantly simpler as that file can just be wiped
out each time instead of worrying about preserving contents.

Signed-off-by: Sandon Van Ness <sandon@inktank.com>
(cherry picked from commit 32c82347259d51d11dcb489149ce8557c9181e6f)