Subscribe to InterfacesAdded/Removed/PropertiesChanged signals before
using GetManagedObjects. For some reason when iwd starts after the
client, we consistently get the managed objects list from before Adapter
interfaces are added but we miss the subsequent InterfacesAdded
signals, probably has to do with the GetManagedObjects and the AddMatch
calls all being synchronous.
Secondly call self.populate_devices() on init as it won't be called if
IWD is not on the bus.
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