virttest: Add functions to remove color codes from Linux console output

Sometimes Linux console output include some escape and sequences
for display. This make the console output hard to read and analyse.
This function will help scripts to remove those special codes.

Also add a function for get the stripped output from sessions on
aexpect.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: Fix the wrong list_nic_addr

Current version make up a wrong list_nic_addr.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: Use get_stripped_output to read from serial console

Use  get_stripped_output to remove the unreadable codes
from the serial console output.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests: Make boot order check fit for qmp monitor

The output from qmp monitor for pci information is different from
human monitor. This help the scripts run correctly with both qmp
and human monitor.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>