Revert "Disable host key checking in nodepool"

This reverts commit 49f721a0ba3531384bfaf920fdf1f4a606e6fa92.

Reason for revert: This did not work as expected -- all connections received a host key verification error.

Change-Id: Id0be45f2c45e61f513d26bb5a6801e145255d484
1 file changed