Rework setNmiProperty to use yielding Dbus API
Rework setNmiProperty to use yielding Dbus API

setNmiProperty was the last holdout making blocking Dbus calls in the
ipmiChassisControl function. This converts the blocking calls to
yielding calls, making use of the Context object.

Tested: ipmitool chassis power diag
        Check host to see that it recieved an NMI

Change-Id: I4d96752b020947cc08a1e985213afc1af735344d
Signed-off-by: Vernon Mauery <4fbc0e9805d36da7c621cd4d73f3eb0d5b12b5f3@linux.intel.com>

openbmc/phosphor-host-ipmid,openbmc/phosphor-host-ipmid,openbmc/phosphor-host-ipmid