misc: CentOSStream => rpm
misc: CentOSStream => rpm

lsb_release -is identifies CentOS 8 Stream as CentOSStream.
Teuthology should recognize this as 'rpm'.

Signed-off-by: Marcus Watts <d0b5f839fb4838f25476cd44c65fa22be736e176@redhat.com>

SUSE/teuthology,ktdreyer/teuthology,SUSE/teuthology,dmick/teuthology,ceph/teuthology,SUSE/teuthology,ceph/teuthology,dmick/teuthology,ktdreyer/teuthology,dmick/teuthology