Import portage when it's used to fix broken tree.

This is just a temporary workaround until buildbots have portage installed
outside the chroot. We should roll this back when that's fixed.

TBR=sosa@chromium.org
BUG=b0rked tree
TEST=ran unit tests

Change-Id: I004c1476e929212774218d50d10f371806cf6c7f

Review URL: http://codereview.chromium.org/4070002

cros_mark_as_stable.py

@@ -14,7 +14,6 @@ import re
 import shutil
 import subprocess
 import sys
-from portage.versions import pkgsplit, pkgsplit, vercmp
 
 sys.path.append(os.path.join(os.path.dirname(__file__), 'lib'))
 from cros_build_lib import Info, RunCommand, Warning, Die
@@ -74,6 +73,7 @@ def _Print(message):
 
 def _BestEBuild(ebuilds):
   """Returns the newest EBuild from a list of EBuild objects."""
+  from portage.versions import vercmp
   winner = ebuilds[0]
   for ebuild in ebuilds[1:]:
     if vercmp(winner.version, ebuild.version) < 0:
@@ -279,6 +279,7 @@ class _EBuild(object):
     Uses equery to find the ebuild path and sets data about an ebuild for
     easy reference.
     """
+    from portage.versions import pkgsplit
     self.ebuild_path = path
     (self.ebuild_path_no_revision,
      self.ebuild_path_no_version,