Don't unpack files to system root

When unpacking a file that is in root, it got a temporary file
name /.apk...  however if the --root option was used it should
have the name root/.apk... otherwise unpacking will fail if the
user does not have write access to /.

Signed-off-by: Fredrik Gustafsson <fredrigu@axis.com>
2 jobs for master
Status Job ID Name Coverage
  Test
failed #16483
docker-alpine
test:alpine

failed #16484
x86_64 docker-alpine
test:debian

 
Name Stage Failure
failed
test:debian Test There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log
failed
test:alpine Test There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log