cros_workon: modify regen_manifest_and_sync to use loman
cros_workon: modify regen_manifest_and_sync to use loman

This fixes a bug where user added local_manifest.xml entries
get clobbered.

BUG=5787
TEST=Verified start of various packages works correctly.

Change-Id: I2348dfb1be098b81ede5928426192c655160564d

Review URL: http://codereview.chromium.org/3389013

vmware/coreos-scripts,andrejro/coreos--scripts,marineam/coreos-scripts,mischief/scripts,andrejro/coreos--scripts,gtank/scripts,coreos/scripts,bcwaldon/coreos-scripts,glevand/coreos--scripts,vmware/coreos-scripts,mjg59/scripts,trnubo/scripts,BugRoger/scripts,zhang0137/scripts,trnubo/scripts,mjg59/scripts,zhang0137/scripts,smilart/scripts,fivethreeo/scripts,crawford/scripts,fivethreeo/scripts,mischief/scripts,sigma/coreos-scripts,nicescale/scripts,endocode/scripts,zhang0137/scripts,coreos/scripts,trnubo/scripts,glevand/coreos--scripts,andrejro/coreos--scripts,crawford/scripts,BugRoger/scripts,BugRoger/scripts,nicescale/scripts,smilart/scripts,endocode/scripts,bcwaldon/coreos-scripts,endocode/scripts,gtank/scripts,mjg59/scripts,gtank/scripts,smilart/scripts,vmware/coreos-scripts,sigma/coreos-scripts,marineam/coreos-scripts,mischief/scripts,marineam/coreos-scripts,nicescale/scripts,fivethreeo/scripts,crawford/scripts,sigma/coreos-scripts,bcwaldon/coreos-scripts