Reland of Disable Goma for Linux32 (ARM) bots. (patchset #1 id:1 of https://codereview.webrtc.org/2910963002/ )

Reason for revert:
Moving back again since I see many failures on our trybot trying to roll:
https://build.chromium.org/p/tryserver.webrtc/builders/linux32_arm_dbg/builds/30/

Original issue's description:
> Revert of Disable Goma for Linux32 (ARM) bots. (patchset #1 id:1 of https://codereview.webrtc.org/2911893002/ )
>
> Reason for revert:
> According to crbug.com/726706 this is now fixed so let's give it a try.
>
> Original issue's description:
> > Disable Goma for Linux32 (ARM) bots.
> >
> > This config is having issues to build reliably on Goma.
> >
> > BUG=chromium:726706
> > TBR=mbonadei@webrtc.org
> >
> > Review-Url: https://codereview.webrtc.org/2911893002 .
> > Cr-Commit-Position: refs/heads/master@{#18295}
> > Committed: 3a343ad329
>
> TBR=mbonadei@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=chromium:726706
>
> Review-Url: https://codereview.webrtc.org/2910963002
> Cr-Commit-Position: refs/heads/master@{#18299}
> Committed: fd1ff9b881

TBR=mbonadei@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:726706

Review-Url: https://codereview.webrtc.org/2908143002
Cr-Commit-Position: refs/heads/master@{#18301}

tools_webrtc/mb/mb_config.pyl

@@ -201,8 +201,9 @@
     'gcc_release_bot_x64': [
       'gn', 'gcc', 'release_bot', 'x64'
     ],
+    # TOOD(kjellander): Restore Goma for this when crbug.com/726706 is fixed.
     'debug_bot_arm': [
-      'gn', 'openh264_debug_bot', 'arm'
+      'gn', 'openh264', 'debug', 'arm'
     ],
     'release_bot_arm': [
       'gn', 'openh264_release_bot', 'arm'