fix is_fedora for centos 8 stream
fix is_fedora for centos 8 stream

When deploying on the centos 8 stream variant
the output of "lsb_release -i -s" is
CentOSStream instead of CentOS

This breaks the is_fedora function in devstack
preventing package installation and removal.

Change-Id: I39ccefbd06f46adf5077f8d8001f37d3b190f040

nawawi/openstack,nawawi/openstack,openstack-dev/devstack,openstack-dev/devstack