build: fix missing python libraries from rpm

the files listed below where not included in the final rpm
bacuse they where installed in $(PKGROOT) and not in
$(ROOT)/$(PKGROOT)

/opt/rocks/lib/python2.6/site-packages
/opt/rocks/lib/python2.6/site-packages/drv_libxml2.py
/opt/rocks/lib/python2.6/site-packages/drv_libxml2.pyc
/opt/rocks/lib/python2.6/site-packages/drv_libxml2.pyo
/opt/rocks/lib/python2.6/site-packages/libxml2.py
/opt/rocks/lib/python2.6/site-packages/libxml2.pyc
/opt/rocks/lib/python2.6/site-packages/libxml2.pyo
/opt/rocks/lib/python2.6/site-packages/libxml2mod.a
/opt/rocks/lib/python2.6/site-packages/libxml2mod.la
/opt/rocks/lib/python2.6/site-packages/libxml2mod.so
python-extra: add sqlalchemy