so apt sees the expanded list

so we can manipulate boot.scr from the board

This allows us to override bootargs from the u-boot prompt like

  setenv bootargs foo bar

to simplify debugging in Jenkins

We want it for all apt invocations

and remove unused ones

before building the image

In case of vmdeboostrap_opts use a shell array to indicate that we want
to expand.

instead of the global pureos_board

to not fail on paths with spaces

to ease debugging in Jenkins

to make shell's '-u' happy.

This allows us to pass in e.g. -j

to work around #887892

vmdebootstrap wants UEFI for arm64 and we can use the Debian kernel when we
only run in qemu.