docs/debugging.md: drop --privileged from dbuild start instructions
docs/debugging.md: drop --privileged from dbuild start instructions

Instead, label the mapped volume by passing `:z` options to `-v`
argument, like we do for other mapped volumes in the `dbuild` script.
Passing the `--privileged` flag doesn't work after the most recent
Fedora update and anyway, using `:z` is the proper way to make sure the
mounted volume is accessible. Historically it was needed to be able to
open cores as well, but since 5b08e91bd this is not necessary as the
container is created with SYS_PTRACE capability.

Signed-off-by: Botond Dénes <a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>
Message-Id: <20200703072703.10355-1-a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>

avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla