Can't interpolate variables

[lis0r]

The variable interpolation for file_unarchive_cmd can only replace entire parameters, not interpolate them. e.g., the following fails:

"file_unarchive_cmd": ["7z", "x", "$ARCHIVE_PATH", "DietPi_RPi-ARMv8-Buster.img", "-o$TMP_DIR"],

7z insists on -o being one argument.

[mkaczanowski]

this is implemented as a simple substitution:

packer-builder-arm/builder/step_populate_filesystem.go

Line 34 in 7d1d806

vars := map[string]string{

it should be trivial to change @lis0r if you need it