install & run ntpclient to make sure boot2docker's clock is set

I couldn't get Chef to run in boot2docker-hosted containers because the clock in the VM was too skewed. Apparently you can sync the VM clock with the host's using VirtualBox guest additions, but I'm assuming those aren't installed in boot2docker.

This installs the ntpclient package in Tiny Core and runs it against pool.ntp.org in bootsync.sh.