packagecmd: Always use buildsys++ environment variables
packagecmd: Always use buildsys++ environment variables

Currently we only use the environment variables used to run buildsys++ if
a PackageCmd has specified it's own environment variables. For consistency
always use the buildsys++ environment variables for commands.

Change-Id: I553a8bfe6cb20782c27fe286fdb73df5ed05e45b
Reviewed-by: Scott Parlane <85029adc3fa41ef14594a57826619713bfe95f25@alliedtelesis.co.nz>
Signed-off-by: Matt Bennett <e3d8681cec70d3da741935b3385821001b249adc@alliedtelesis.co.nz>

ATL-NZ/buildsyspp,alliedtelesis/buildsyspp