Issue #222: add python-xml to suse require list

check on suse
xml.etree module is from python-xml on suse.
need to add python-xml to require list

This is different from fedora distro.
xml.etree module is from python standlib python-libs on fedora

issue:
https://github.com/kimchi-project/kimchi/issues/222

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>