Use rdeps option correctly.
Use rdeps option correctly.

By default parallel_emerge gives the union of DEPEND and RDEPEND. With --rdeps
the utility and parallel_emerge use just RDEPEND.

BUG=chromium-os:13448
TEST=ran the utility

Change-Id: I8334824b6c9a9bfaa03c78918414ca9e40811493

Review URL: http://codereview.chromium.org/6736015

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