Fix docker image running with zap user instead of root

What does this MR do?

Found that dast image is running with root privileges. This can be checked running image in interactive mode:

root@7020cd870424:/output# id uid=0(root) gid=0(root) groups=0(root)

As changed now the image is running with user zap:

zap@a1cd694150ba:/output$ id uid=1000(zap) gid=1000(zap) groups=1000(zap)