Support `abuild-rootbld`

[orhun]

See abuild-rootbld.

At first try, I got a bunch of errors:

fatal: not a git repository (or any of the parent directories): .git
>>> ERROR: zps: rootbld: /home/orhun/apkbuilds/zps/apkbuilds/.rootbld-repositories does not exist

• rootbld expects a git repository (most likely aports)

bwrap: No permissions to creating new namespace, likely because the kernel does not allow non-privileged user namespaces. On e.g. debian this can be enabled with 'sysctl kernel.unprivileged_userns_clone=1'.

• See https://github.com/containers/bubblewrap/issues/324#issuecomment-517378834

bwrap: Creating new namespace failed: Operation not permitted

Further investigation is needed.