content dirs: skip creation if either mkdir or create-subdirs is false

content dirs: skip creation if either mkdir or create-subdirs is false

This is slightly confusing due to both options, the legacy convoluted
one and the new targeted one, exist, but before the rework we skip if
either of those sub-expressions was true, so doing it needs both to
be true.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>