selftests/functional/test_interrupt.py: silence the test

When running this functional test with the standard unittest
discovery/runner it produces output that conflicts with the runner
output.

It looks like this output is not necessary for the test itself, and
not that helpful for debugging purposes, so, let's just silence it.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

selftests/functional/test_interrupt.py

@@ -3,7 +3,6 @@ import sys
 import tempfile
 import time
 import shutil
-import logging
 
 import aexpect
 import psutil
@@ -72,8 +71,7 @@ class InterruptTest(unittest.TestCase):
                                   bad_test.path,
                                   bad_test.path,
                                   bad_test.path))
-        proc = aexpect.Expect(command=cmd_line, linesep='',
-                              output_func=logging.critical)
+        proc = aexpect.Expect(command=cmd_line, linesep='')
         proc.read_until_last_line_matches(os.path.basename(bad_test.path))
         proc.sendline('\x03')
         proc.read_until_last_line_matches('Interrupt requested. Waiting 2 '
@@ -113,8 +111,7 @@ class InterruptTest(unittest.TestCase):
                                   good_test.path,
                                   good_test.path,
                                   good_test.path))
-        proc = aexpect.Expect(command=cmd_line, linesep='',
-                              output_func=logging.critical)
+        proc = aexpect.Expect(command=cmd_line, linesep='')
         proc.read_until_last_line_matches(os.path.basename(good_test.path))
         proc.sendline('\x03')
         proc.read_until_last_line_matches('TIME       : %d s')