virt.shared.cfg.base:Avoid to add more disk in blacklist

Currently, autotest use such as /dev/sda.* to get the disk of
the blacklist, but this will raise an error if the disk 'sdaa'
or some name like this, it's not correct as we just want to add
sda or name like sda1-9 to the blacklist.

change the pattern to /dev/sda[\d]* can avoid this.

Signed-off-by: Mike Qiu<qiudayu@linux.vnet.ibm.com>