adding ability to enable command argument processing via nrpe client

Signed-off-by: Nick Chappell <nick@intronic.org>

Taken from: https://github.com/Icinga/puppet-icinga2/pull/22
fixing missing parameter name

Signed-off-by: Nick Chappell <nick@intronic.org>

Taken from: https://github.com/Icinga/puppet-icinga2/pull/22
update README with new argument instructions

Signed-off-by: Nick Chappell <nick@intronic.org>

Taken from: https://github.com/Icinga/puppet-icinga2/pull/22
fixing typo with Determines

Signed-off-by: Nick Chappell <nick@intronic.org>

Taken from: https://github.com/Icinga/puppet-icinga2/pull/22