Test multipathd_topology() and fix it for Python3

tests/integration/dom0-template/usr/sbin/multipathd

@@ -0,0 +1,2 @@
+#!/bin/sh
+echo -n "${0##*/}$*"

tests/unit/test_process_output.py

@@ -12,3 +12,8 @@ def test_module_info(bugtool, dom0_template):
     bugtool.PROC_MODULES = dom0_template + "/proc/modules"
     output = bugtool.module_info(bugtool.CAP_KERNEL_INFO)
     assert output == "modinfo for tcp_diag\nmodinfo for udp_diag\nmodinfo for inet_diag\n"
+
+
+def test_multipathd_topology(bugtool, dom0_template):
+    """Assert multipathd_topology() returning the output of the faked multipathd tool"""
+    assert bugtool.multipathd_topology(bugtool.CAP_MULTIPATH) == bugtool.MULTIPATHD + "-k"

xen-bugtool

@@ -1525,9 +1525,15 @@ def csl_logs(cap):
     return output.getvalue()
 
 def multipathd_topology(cap):
-    pipe = Popen([MULTIPATHD, '-k'], bufsize=1, stdin=PIPE,
-                     stdout=PIPE, stderr=dev_null)
-    stdout, _ = pipe.communicate('show topology')
+    pipe = Popen(
+        [MULTIPATHD, "-k"],
+        universal_newlines=sys.version_info > (3, 0),
+        bufsize=1,
+        stdin=PIPE,
+        stdout=PIPE,
+        stderr=dev_null,
+    )
+    stdout, _ = pipe.communicate("show topology")
 
     return stdout