Update parallel_emerge to make use of new features in Portage 2.1.9.48.
Update parallel_emerge to make use of new features in Portage 2.1.9.48.

What's new?
 - PORTAGE_LOCKS=false is now safe to use for host emerges
 - FEATURES=parallel-install is now used
 - FEATURES=-ebuild-locks is now used for board installs.
 - build_image and make_chroot are now 20% faster.

BUG=None
TEST=make_chroot, build_packages, build_image
Change-Id: Iae99012951d286f81fd655f88150b868bb16a564
Reviewed-on: http://gerrit.chromium.org/gerrit/599
Reviewed-by: Nick Sanders <f4566bb3c90c0bf5fa0906b296b1da45051a62ee@chromium.org>
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

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