.contrib.charmsupport.nrpe.NRPE.write to preserve old entries in the monitors key

[auria]

When running the following, all entries on the monitors keymap will be overrid.

nrpe_setup = NRPE()
nrpe_setup.add_check(shortname='test', description='test desc', check_cmd='')
nrpe_setup.write()

The PR on #311 will preserve old entries provided nrpe_setup.remove_check(shortname='test') has not been called. Otherwise, it will remove the expected checks but it will preserve the rest.

[auria]

This patch has been merged into master, but it has not been released yet.

[auria]

Released on 0.19.14