build/base: install ntpstat on Debian plateforms

"ntpstat" is not packaged in Debian. This patch aims to take the official
binary from github and move it in /usr/sbin which other ntp tools.

This binary is useful to check if client is synchronized with the server
by returning a return code.

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>