virttest: Update nfs to fit the modification in service.py

Recently the return value of status function in service.py is modified. This function
will only return True or False instead of the command output. So update related
code in nfs.py

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
virttest: Use makedirs instead of mkdir in nfs.py

Use makedirs to create a leaf directory and all intermediate ones. Also
create the mount_dir if it doesn't exist.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
virttest: Update nfs exported

As one entry of nfs exported fs from "exportfs -v" output may be splited to
two lines, use re.findall() to get the entries instead of splitlines.

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

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