virttest.virt_vm: Add support for logging via serial after remote login fail

To keep cases not related with nics can run under a bad network
condition.

Also update the interface to date.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Signed-off-by: Yiqiao Pu <ypu@redhat.com>
virttest.virt_vm: Add support for restarting guest network via serial console

This patch will add a parameter to serial_login function, when set this parameter,
autotest will try to restart guest's network after serial login, then try to login
via network again.

This patch maybe help in some network related tests, such as file_transfer....

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
virttest.virt_vm: Update get_memory_size

In Windows guests, wmic will be auto installed in the first use, it may cause
get_memory_size() timeout. This patch just set get_memory_size timeout to 60s.

Also add a parameter re_str for get_memory_size for different guests.
Default value for mem_chk_re_str is ([0-9]+)

Signed-off-by: Suqin Huang <shuang@redhat.com>
Signed-off-by: Feng Yang <fyang@redhat.com>
virttest.virt_vm: small bug fix

Fix the format problem and typo in this file.

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