Currently a new connection is created for every API call which is
never closed. This results in open connections accumulating over time
due to periodic calls like power state polling, which is further
compounded by the number of ovirt nodes deployed.
This change converts _getvm into a generator based context manager so
that the connection can be closed after every call.
Change-Id: I30f9695c591f72dae21467b0b31f6f67fad7cc8a
(cherry picked from commit 343a57570e)
b7ba3653fd