ntp-converge: Add MINMAXPOLL definition to allow setting min and max poll intervals

Since we generate our own ntp.conf allow min/maxpoll values to be set for
the server.

Signed-off-by: John Stultz <john.stultz@linaro.org>
drift-log: Make sure we record the hostname in the log

Getting confused occasionally with lots of log files around,
so add the hostname to help sort things out.

Signed-off-by: John Stultz <john.stultz@linaro.org>