test_decryption_failure is quite simple and only verifies that a known
network exists after starting. This causes the test to end before IWD can
fully start up leaving the DBus utilities in limbo having not fully
initialized.
Then, on the next test, stale InterfaceAdded signals arrive (for Station
and P2P) which throw exceptions when trying to get the bus (since IWD is
long gone). In addition the next IWD instance has started so any paths
included in the InterfaceAdded signals are bogus and cause additional
exceptions.
At the end of this test we can call list_devices() which will wait for
the InterfaceAdded signal, and cleanly exit afterwards.
