[ansible/library/exabgp]: Output handling for PY3 (sonic-net#14423)

Tests running in PTF Py3 only image fail with error -

E           {"changed": false, "failed": true, "msg": "Error: (<class 'AttributeError'>, AttributeError(\"'str' object has no attribute 'decode'\"), <traceback object at 0x7f60a07fe2c0>)"}

How did you do it?
Fixed to code to treat output as UTF-8 native string in Py3.

How did you verify/test it?
By running failed tests manually on a testbed.

ansible/library/exabgp.py

@@ -172,7 +172,12 @@ def exec_command(module, cmd, ignore_error=False, msg="executing command"):
 
 def get_exabgp_status(module, name):
     output = exec_command(module, cmd="supervisorctl status exabgp-%s" % name)
-    m = re.search(r'^([\w|-]*)\s+(\w*).*$', output.decode("utf-8"))
+    m = None
+    if six.PY2:
+        m = re.search(r'^([\w|-]*)\s+(\w*).*$', output.decode("utf-8"))
+    else:
+        # For PY3 module.run_command encoding is "utf-8" by default
+        m = re.search(r'^([\w|-]*)\s+(\w*).*$', output)
     return m.group(2)