Fix typo in install-sysroot.py

Fix typo in install-sysroot.py

install-sysroot.py was intended to default to installing
the sysroot ia32, but within this script 'i386' is used to
refer to this architecture.

This most likely went unnoticed since the ia32 builder
either use branding=Official, or explicitly set
use_sysroot=1, or have a complete set of packages for
cross building on the host system.

BUG=504446
Committed: https://crrev.com/1d62049b4c176fbd43bed90fc9a76273b11ad406
Cr-Commit-Position: refs/heads/master@{#347821}

[Sam Clegg, 2015-09-08 11:06:59]

sbc@chromium.org changed reviewers:
+ dpranke@chromium.org

[Sam Clegg, 2015-09-08 11:07:22]

The CQ bit was checked by sbc@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-08 11:07:29]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1317973005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1317973005/20001

[commit-bot: I haz the power, 2015-09-08 11:24:29]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-08 11:24:30]

Dry run: This issue passed the CQ dry run.

[Dirk Pranke, 2015-09-08 20:18:45]

looks like a bug, alright.

lgtm.

[Sam Clegg, 2015-09-08 22:55:20]

The CQ bit was checked by sbc@chromium.org

[commit-bot: I haz the power, 2015-09-08 22:55:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1317973005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1317973005/20001

[commit-bot: I haz the power, 2015-09-08 23:02:56]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-08 23:03:28]

Patchset 2 (id:??) landed as
https://crrev.com/1d62049b4c176fbd43bed90fc9a76273b11ad406
Cr-Commit-Position: refs/heads/master@{#347821}

[chrishtr, 2015-09-08 23:57:38]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1315773003/ by chrishtr@chromium.org.

The reason for reverting is: Caused check_licenses to fail:

https://build.chromium.org/p/chromium/builders/Linux/builds/66701

.