WebRTC: Reshuffle Mac slaves in client.webrtc

WebRTC: Reshuffle Mac slaves in client.webrtc

After adding the GN bots for Mac, we ended up with
too many checkouts on the slave machines.
This should reduce the number to max two checkouts.

This is similar to https://codereview.chromium.org/883633002

TBR=phoglund@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=293823

[kjellander_chromium, 2015-01-27 13:37:24]

The CQ bit was checked by kjellander@chromium.org

[commit-bot: I haz the power, 2015-01-27 13:37:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/865783003/1

[commit-bot: I haz the power, 2015-01-27 13:39:07]

Committed patchset #1 (id:1) as
http://src.chromium.org/viewvc/chrome?view=rev&revision=293823

[kjellander_chromium, 2015-01-27 13:49:18]

On 2015/01/27 13:39:07, I haz the power (commit-bot) wrote:
> Committed patchset #1 (id:1) as
> http://src.chromium.org/viewvc/chrome?view=rev&revision=293823

We're really in a lack of Mac slaves, but I filed a ticket to get more VMs at
least.
One VM is also borrowed to
http://build.chromium.org/p/client.webrtc.fyi/waterfall to try out parallel test
execution...