Make two calls synchronous and also make

RemoteActivatable::activatableType() return a sane default in case of
errors.

activatableType() was returning
Knm::Activatable::WirelessInterfaceConnection in case of error or when
the assynchronous DBus call returned before the real value was
available, which led to a crash in applet/wirelessstatus.cpp when the
real activatable type was not WirelessInterfaceConnection ot
WirelessNetwork.

BUG: 283241
FIXED-IN: 0.9.0
(cherry picked from commit ca33e27e)