common: Don't delete /dev/ content but the directory

Deleting ${dir}/dev/* leads to a very long string to rm that
- confuse the reading
- might trigger the max length of args to rm

As an example we had :
rm -rf /run/shm/var/lib/debootstrap/all-ubuntu/install/eDeploy-Build-All-OpenStack-Ubuntu/pxe.temp/dev/MAKEDEV /run/shm/var/lib/debootstrap/all-ubuntu/install/eDeploy-Build-All-OpenStack-Ubuntu/pxe.temp/dev/autofs /run/shm/var/lib/debootstrap/all-ubuntu/install/eDeploy-Build-All-OpenStack-Ubuntu/pxe.temp/dev/block ....

So let's delete the directory and recreate it. That will not flood the logs.