test/common: update vfio-user capable Qemu branch

This should be vfio-user-master now. vfio-user-v0.6
branch is obsolete.

Signed-off-by: Karol Latecki <karol.latecki@intel.com>
Change-Id: Iaa0b429c4de13c59e1f58fe59149367f941d42f2
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/8062


Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Ziye Yang <ziye.yang@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Michal Berger <michalx.berger@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>