Use full clone in propose requirements updates

Shallow (--depth=1) clone raises some problems with git review tool.

Here is the part of the failed propose-requirements-update job logs:

  + git clone --depth=1 ssh://jenkins@review.openstack.org:29418/openstack/cinder.git
  + pushd cinder
  + git review -s
  + git review -d I2d8f240009d2f847b321baa011880f753783be83
  Downloading refs/changes/69/60969/1 from gerrit into review/jenkins/openstack/requirements
  fatal: unresolved deltas left after unpacking
  fatal: unpack-objects failed

Change-Id: Ie69261fde73c18134906f3edd1263479830005c4