cbuildbot: Increase timeout for R46 canaries

BuildPackages takes about 50 more minutes on R46 than expected. Celes
tests are timing out. For now, we can just increase the timeout.
Ultimately we need to find out why BuildPackages is taking extra time.

BUG=chromium:540740
TEST=None

Change-Id: I933dcced8fa56df62a0fbbd3f6c3d8a9fdefad72
Reviewed-on: https://chromium-review.googlesource.com/304791
Reviewed-by: David James <davidjames@chromium.org>
Commit-Queue: Paul Hobbs <phobbs@google.com>
Tested-by: Paul Hobbs <phobbs@google.com>
1 file changed