Make parallel_emerge less verbose -- only update every 15 seconds.
Make parallel_emerge less verbose -- only update every 15 seconds.

Right now, parallel_emerge prints status updates every 5 seconds. This
can be a bit too verbose so I've updated it to only update every 15
seconds.

To ensure additional jobs are still scheduled regularly when the
--load-average option is used, I've updated parallel_emerge to still call
the ScheduleLoop once every 5 seconds while it's waiting for jobs to
complete.

BUG=chromium-os:19102
TEST=Run build_packages, watch it be a little less verbose.

Change-Id: If59eeed019129683dae6ce58454e50b3264aea54
Reviewed-on: http://gerrit.chromium.org/gerrit/5897
Reviewed-by: Nick Sanders <f4566bb3c90c0bf5fa0906b296b1da45051a62ee@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,coreos/chromite,zhang0137/chromite,zhang0137/chromite,chadversary/chromiumos.chromite,coreos/chromite,coreos/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite