tests.ethtool: Wait for guest shell prompt when setting ethtool option

Some nic driver would print logs into serial console, so send
a return character then wait for the prompt.

This patch also re-formats the ethtool_set function.

Changes from v3:
 * Add a timeout for waiting the shell prompt.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
tests.ethtool: Update session operation

There could be problem when this test fails, so add
try...except block in the end of this script to avoid
unexpected exception when test fails.

Changes from V1:
 * Rebase this patch against merged tree
 * Verify session before close it.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Acked-by: Feng Yang <fyang@redhat.com>
tests.ethool.py: Add error.context() support

log case steps into logging.info.

Signed-off-by: Feng Yang <fyang@redhat.com>
Acked-by: Suqin Huang <shuang@redhat.com>
test.cfg.ethtool: Update guest realted params

Update ethtool params for different guest and driver

Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: Xiaoqing Wei <xwei@redhat.com>
libvirt_xml_unittest: Fix module import error

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>