nrpe.NRPE.write doesn't support multiple writes (previous checks will be lost for nagios)

[Alvaro Uria]

Per [1], checks will be configured in /etc/nagios/nrpe.d/check_SHORTNAME.cfg, but they will only be shared with Nagios (via the monitors interface) if all checks are added before nrpe_setup.write().

1) Sample 1 (works fine):
"""
nrpe_setup = nrpe.NRPE()
nrpe_setup.add_check(shortname='test1', description='test1 desc', check_cmd='check_test.py')
nrpe_setup.add_check(shortname='test2', description='test2 desc', check_cmd='check_test.py')
nrpe_setup.write()
"""

2) Sample 2 (only test2 will be configured in nagios):
"""
def func(name):
    nrpe_setup = nrpe.NRPE()
    nrpe_setup.add_check(shortname=name, description='test desc', check_cmd='check_test.py')
    nrpe_setup.write()

func('test1')
func('test2')
"""

I think the NRPE class should support a "clear" method or already existing checks should be kept.

OTOH: nrpe-external-master interface [2] doesn't support such relation data.

1. https://github.com/juju/charm-helpers/blob/master/charmhelpers/contrib/charmsupport/nrpe.py#L285
2. https://github.com/cmars/nrpe-external-master-interface/blob/master/provides.py