fixed problem with default behavior which was broken in latest
commit.

TEST=tested the following behaviors:
./setup_chromeos.py --dir /tmp/x
./setup_chromeos.py --dir /tmp/x --version=latest_common
./setup_chromeos.py --dir /tmp/x --version=latest_lkgm
./setup_chromeos.py --dir /tmp/x --version=top
./setup_chromeos.py --dir /tmp/x --version=top --timestamp=1361921045
./setup_chromeos.py --dir /tmp/x --version=lkgm --timestamp=1361921045
./setup_chromeos.py --dir /tmp/x --version=lkgm --timestamp=1356508800
./setup_chromeos.py --dir /tmp/x --version=common --timestamp=1356508800

PRESUBMIT=passed
R=asharif,yunlian,shenhan
APPROVED=asharif
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=66090-p2
RCL=66094-p2
RDATE=2013/02/26 16:30:29


P4 change: 43143278
diff --git a/v14/setup_chromeos.py b/v14/setup_chromeos.py
index 1938d7d..d7be036 100755
--- a/v14/setup_chromeos.py
+++ b/v14/setup_chromeos.py
@@ -86,7 +86,7 @@
   parser = optparse.OptionParser()
   parser.add_option("--dir", dest="directory",
                     help="Target directory for ChromeOS installation.")
-  parser.add_option("--version", dest="version", default="latest",
+  parser.add_option("--version", dest="version", default="latest_lkgm",
                     help="""ChromeOS version. Can be:
 (1) A release version in the format: 'X.X.X.X'
 (2) 'top' for top of trunk