Revert of Only run install-debian.wheezy.sysroot.py once during runhooks

Revert of Only run install-debian.wheezy.sysroot.py once during runhooks (patchset #2 id:20001 of https://codereview.chromium.org/834133003/)

Reason for revert:
See failing gclient runhooks after this patch and the Chrome build tree turned red (see http://build.chromium.org/p/chromium.win/waterfall?builder=Win8%20GN for details).

I can't find any other reason for this failure and will will try to revert.

Original issue's description:
> Only run install-debian.wheezy.sysroot.py once during runhooks
>
> This script was previously run three times, once for
> each arch, with two of the three always being no-ops.
>
> Instead just run the script once and have the script
> figure out which image to download.
>
> TEST=trybots + 'gclient runhooks' locally
>
> Committed: https://crrev.com/711802679ce2feb228ad418dd117ae23301e5c02
> Cr-Commit-Position: refs/heads/master@{#310467}

TBR=thestig@chromium.org,sbc@chromium.org
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/9c5c0565bfe3b438b018fc284f752f7766fdd9ea
Cr-Commit-Position: refs/heads/master@{#310468}

[henrika (OOO until Aug 14), 2015-01-08 10:46:14]

Created Revert of Only run install-debian.wheezy.sysroot.py once during runhooks

[commit-bot: I haz the power, 2015-01-08 10:47:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/843683003/1

[commit-bot: I haz the power, 2015-01-08 10:49:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-08 10:50:24]

Patchset 1 (id:??) landed as
https://crrev.com/9c5c0565bfe3b438b018fc284f752f7766fdd9ea
Cr-Commit-Position: refs/heads/master@{#310468}