qemu.tests: Add a kvm subtest format_disk.

This test will simply create a file system on disk, mount it and write
a file with some content to the disk. Check whether the write could be
succeeded.

Signed-off-by: sshang <sshang@redhat.com>

Checking guest os type with 'guest_name' parameter may not
always work for all guests, and not supported by upstream.
Thus update all these places to using 'os_type'.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>

In the format disk test, the status of the harddisk is different in different
env in Windows guest. Should check if the disk plused is offline and writeable.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>

This patch try to fix all the tab and trailing space problems.

Signed-off-by: Jason Wang <jasowang@redhat.com>

Make command timeout of format_disk.py scirpt longer and configurable

Signed-off-by: Feng Yang <fyang@redhat.com>