Allow specifying ownership and mode of custom airootfs files and directories

profiledef.sh can now contain an associative array called file_permissions which can be used to set custom ownership and mode of custom airootfs files. The array's keys contain the path and the value is a colon separated list of owner UID, owner GID and access mode.
For example:

    file_permissions=(
      ["/etc/shadow"]="0:0:400"
    )

This means that mkarchiso now copies airootfs files (and directores) without permissions and anything that should be owned by a user other than root and/or if the mode should be something other than 644 for files and 755 for directories must to be listed in ${file_permission[@]} in profiledef.sh.

Fixes archlinux/archiso#61 .
1 job for airootfs-permissions-and-ownership in 13 seconds (queued for 2 seconds)