ignore ntp check because it's flapping to often (Bug #6407)

Change-Id: I52e19bbdfcf6576bd9c247d99aace47eb86c8116
Increase nagios max_checks_attempts from 1 to 4 so notifications won't be sent out on first failed check_mk check (Bug #6461)

Change-Id: I1bd47b3c3d17508488a4db90d74118006d85a03a