CHROMIUM: Restrict environment import.

Change upstart to only import externally supplied variables into the
job environment if the job explicitly declares them using the import
statement.

BUG=chromium:818032
TEST=Image boots and passes tests.

Reviewed-on: https://chromium-review.googlesource.com/1013931
Change-Id: I44b453605232562099c1c1d8a4b3b1a1ddc00b5b
1 file changed