virt.virttest.storage: Change the cmp method of the sorted function

Currently, function sorted inside the python was not suitable for
storage, for example, if ls -1d /dev/sd* gets result like this
after split('\n'):
['/dev/sda', '/dev/sda1', '/dev/sda2', '/dev/sda3',
 '/dev/sdaa', '/dev/sdab','/dev/sdac', '/dev/sdad', '/dev/sdae',
 '/dev/sdaf', '/dev/sdag', '/dev/sdah', '/dev/sdai', '/dev/sdaj',
 '/dev/sdak', '/dev/sdal', '/dev/sdam', '/dev/sdan', '/dev/sdao',
 '/dev/sdap', '/dev/sdaq', '/dev/sdar', '/dev/sdas', '/dev/sdb',
 '/dev/sdb1', '/dev/sdb2', '/dev/sdb3', '/dev/sdc', '/dev/sdd',
 '/dev/sde', '/dev/sdf', '/dev/sdg', '/dev/sdg1', '/dev/sdg2',
 '/dev/sdg3', '/dev/sdh', '/dev/sdh1', '/dev/sdh2', '/dev/sdh3',
 '/dev/sdi', '/dev/sdj', '/dev/sdk', '/dev/sdl', '/dev/sdm',
 '/dev/sdn', '/dev/sdo', '/dev/sdp', '/dev/sdq', '/dev/sdr',
 '/dev/sds', '/dev/sdt', '/dev/sdu', '/dev/sdv', '/dev/sdw',
 '/dev/sdx', '/dev/sdy', '/dev/sdz']

it will make no any change if just use sorted. As the default,
it will choose last 9 disk:
['/dev/sdr', '/dev/sds', '/dev/sdt', '/dev/sdu', '/dev/sdv', '/dev/sdw',
 '/dev/sdx', '/dev/sdy', '/dev/sdz']

Sometimes this is very dangerous, for lots of them may be the disk contains
lots of important data. Actually, maybe you just use scsi_debug just create:
['/dev/sdak','/dev/sdal', '/dev/sdam', '/dev/sdan', '/dev/sdao',
 '/dev/sdap', '/dev/sdaq', '/dev/sdar', '/dev/sdas']

But select the wrong disks as mentioned above.

To solve this problem, add param cmp to sorted and get the right order.

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
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>
virt.virttest.storage:avoid the wrong to raise an error

Currently, it will rase and error when '/dev/sdaa' match the pattern
of the blacklist. This should not be happen as we just want sda sda1
and so on to be in the blacklist.

add one more check to avoid this error.

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