More specific lxml versions in tools/pip-requires
More specific lxml versions in tools/pip-requires

Changed lxml version in tools/pip-requires from >=2.3,<3 to
>=2.3,<2.3.5.  pip was apparently accepting 3.0alpha as a <3 requirement
but the ordering of elements changes in that version.  Some of the
libvirt tests would pass with lxml 3.0alpha but fail with any 2.3.x
version.  The tests now pass with any version of lxml within the range
specified.

Change-Id: I2d84d32f1bf6fba2c6dbe05799a284a44d4c39d8

n0ano/ganttclient