libvirt_xml.devices: Add slots for channel.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
utils_test.libvirt: Support discard for creating disk xml.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libvirt_xml_unittest.py: Suppress pylint E1003

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #1809 from autotest/fix-pylint-error

libvirt_xml_unittest.py: Suppress pylint E1003
Merge pull request #1784 from yumingfei/discard

libvirt_xml.channel enhancements&Discard configurations
shared/deps/run_autotest/boottool.py: Fix typo

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>