COOK-3636 Allow ntp cookbook to update clock to ntp servers

Adds two new boolean attributes:
node['ntp']['sync_clock'] - When true, this attribute forces the ntp daemon to halt, executes ntpd -q, and then starts the ntp daemon again. This will repeat every Chef run while the boolean remains true.

node['ntp']['sync_hw_clock'] - When true, this attribute runs the command hwclock --systohc on supported operating systems, forcing the hardware clock to sync to the system time. This will repeat every Chef run while the boolean remains true.