[oe] [meta-qt5] qtbluetooth not building against bluez

[michael at losert.org]

I'm using qtbluetooth (qtconnectivity_git.bb) and noticed that it builds 
some kind of empty dummy library.
I then tried building in verbose mode: "bitbake -v qtconnectivity" and 
got the following message in the log:
"Unsupported Bluetooth platform, will not build a working QtBluetooth 
library.
Either no Qt D-Bus found or no BlueZ headers."

My solution was to add
   EXTRA_QMAKEVARS_PRE += "CONFIG+=config_bluez"
to
   recipes-qt/qt5/qtconnectivity_git.bb

after that it worked as expected.
I'm unsure if it's the right thing to do though.

I'm working with yocto 1.8 fido but also checked the master branch which 
doesn't seem to have anything changed related to qtconnectivity.