Provisioning: Install python36-devel to rhel 7.4

The rhel Python3 system package is missing development libs.

Fixes: PYSIDE-996
Change-Id: I3863c85ad04021dd0f0d4af4bae5917a6785a7e1
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@qt.io>

coin/provisioning/qtci-linux-RHEL-7.4-x86_64/04-install-packages.sh

@@ -70,6 +70,7 @@ installPackages+=(speech-dispatcher-devel)
 installPackages+=(python-devel python-pip)
 # Python 3 with python-devel, pip and virtualenv
 installPackages+=(rh-python36)
+installPackages+=(python36-devel)
 # WebEngine
 installPackages+=(bison)
 installPackages+=(flex)