Add dependency on zstandard for Python2 too
Some of the LbNightlyTools tests require lbinstall and run on Python 2, and without the right dependency I get the error
python/LbRPMTools/LHCbCompatSpecBuilder.py:27: in <module>
from .LHCbRPMSpecBuilder import LHCbBaseRpmSpec
python/LbRPMTools/LHCbRPMSpecBuilder.py:26: in <module>
from lbinstall.Installer import Installer
/usr/local/lib/python2.7/site-packages/lbinstall/Installer.py:29: in <module>
from lbinstall.PackageManager import PackageManager
/usr/local/lib/python2.7/site-packages/lbinstall/PackageManager.py:35: in <module>
import lbinstall.rpmfile as rpmfile
/usr/local/lib/python2.7/site-packages/lbinstall/rpmfile/__init__.py:7: in <module>
import zstandard
E ImportError: No module named zstandard