[qemu] Python 3: Update unicode()

Signed-off-by: NXu Han <xuhan@redhat.com>

qemu/tests/qmp_basic.py

+try:
+    unicode
+except NameError:
+    unicode = str
+
+
 def run(test, params, env):
     """
     QMP Specification test-suite: this checks if the *basic* protocol conforms

qemu/tests/qmp_basic_rhel6.py

 import logging
 
 
+try:
+    unicode
+except NameError:
+    unicode = str
+
+
 def run(test, params, env):
     """
     QMP Specification test-suite: this checks if the *basic* protocol conforms