Linux installer: Fix APT_SOURCES and APT_SOURCESDIR paths

Linux installer: Fix APT_SOURCES and APT_SOURCESDIR paths

> In prior versions of Ubuntu/Debian the Dir::Etc apt-config variable
> contained a trailing slash by default. The cronjob at
> /etc/cron.daily/google-chrome was concatenating that variable into a
> path, assuming the trailing slash. But in Ubuntu 16.10, the trailing
> slash is gone. That breaks the path to the list file, and the cronjob
> fails to fix it.
>
> BUG=663069
>
> Review-Url: https://codereview.chromium.org/2482343002
> Cr-Commit-Position: refs/heads/master@{#430771}
>

BUG=663069
TBR=thestig@chromium.org
NOTRY=true
NOPRESUBMIT=true

[Tom Anderson, 2016-11-09 18:13:50]

thomasanderson@chromium.org changed reviewers:
+ thomasanderson@chromium.org

[Tom Anderson, 2016-11-09 18:13:50]

The CQ bit was checked by thomasanderson@chromium.org

[Tom Anderson, 2016-11-09 18:13:50]

lgtm

[commit-bot: I haz the power, 2016-11-09 18:14:23]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-09 18:19:20]

Committed patchset #1 (id:1)

[Lei Zhang, 2016-11-09 19:05:08]

lgtm