Fix running platform2.py outside of an emerge

BUG=chromium:220003
TEST=Build Platform2 host/target using emerge and platform2.py

Change-Id: Ifcc5429aa02229a0fe4297d0fd65adc58f666e63
Reviewed-on: https://gerrit.chromium.org/gerrit/56872
Reviewed-by: Mike Frysinger <[email protected]>
Tested-by: Liam McLoughlin <[email protected]>
Commit-Queue: Liam McLoughlin <[email protected]>
1 file changed