lib: Fix possible race between UPower and Bluez on init

Fix possible race between UPower and Bluez when creating the BluetoothClient.

Bluetooth-DEBUG: Successfully created UpClient
Bluetooth-DEBUG: Got initial list of 2 UPower devices
Bluetooth-DEBUG: Considering UPower device /org/freedesktop/UPower/devices/mouse_dev_11_22_33_44_55_66
Bluetooth-DEBUG: Could not find bluez device for upower device /org/bluez/hci0/dev_11_22_33_44_55_66
Bluetooth-DEBUG: Considering UPower device /org/freedesktop/UPower/devices/mouse_dev_11_22_33_44_55_67
Bluetooth-DEBUG: Could not find bluez device for upower device /org/bluez/hci0/dev_11_22_33_44_55_67
Bluetooth-DEBUG: Adding adapters from ObjectManager
Bluetooth-DEBUG: Inserting adapter :1.2 /org/bluez/hci0 org.bluez.Adapter1
Bluetooth-DEBUG: Setting '/org/bluez/hci0' as the new default adapter
Bluetooth-DEBUG: Emptying list store as default adapter changed
Bluetooth-DEBUG: Coldplugging devices for new default adapter
Bluetooth-DEBUG: Adding device '11:22:33:44:55:66' on adapter '/org/bluez/hci0' to list store
Bluetooth-DEBUG: Adding device '11:22:33:44:55:67' on adapter '/org/bluez/hci0' to list store
Bluetooth-DEBUG: New default adapter so invalidating all the default-adapter* properties

The UpDevices are enumerated before we've even enumerated the Bluetooth adapters, so we don't have any BluetoothDevices to attach the UpDevices to. Wait until we've at least run through setting a default adapter before enumerating the UPower devices.