Make use of python-subprocess32 module if available.

python-subprocess32 [https://code.google.com/p/python-subprocess32/]
is a backport of Python 3.2 subprocess module with:

* Better process forking.
* More reliable when running with threads.

Although we're not going to use any feature of subprocess32,
this change turn it possible to use subprocess32 as a drop-in
replacement for the original subprocess module.
Signed-off-by: NRudá Moura <rmoura@redhat.com>

avocado/aexpect.py

@@ -264,12 +264,16 @@ if __name__ == "__main__":
 
 # The following is the client part of the module.
 
-import subprocess
 import time
 import signal
 import re
 import threading
 
+try:
+    import subprocess32 as subprocess
+except ImportError:
+    import subprocess
+
 from avocado.utils import astring
 from avocado.utils import data_factory
 from avocado.utils import io

avocado/gdb.py

@@ -25,7 +25,11 @@ import fcntl
 import socket
 import tempfile
 import commands
-import subprocess
+
+try:
+    import subprocess32 as subprocess
+except ImportError:
+    import subprocess
 
 from avocado.utils import network
 from avocado.external import gdbmi_parser

avocado/sysinfo.py

@@ -16,9 +16,13 @@ import gzip
 import logging
 import os
 import shutil
-import subprocess
 import time
 
+try:
+    import subprocess32 as subprocess
+except ImportError:
+    import subprocess
+
 from avocado import utils
 from avocado.linux import software_manager
 from avocado.core import output

avocado/utils/process.py

@@ -20,13 +20,19 @@ import logging
 import os
 import StringIO
 import signal
-import subprocess
 import time
 import stat
 import shlex
 import shutil
 import threading
 
+try:
+    import subprocess32 as subprocess
+    SUBPROCESS32_SUPPORT = True
+except ImportError:
+    import subprocess
+    SUBPROCESS32_SUPPORT = False
+
 from avocado import gdb
 from avocado import runtime
 from avocado.core import exceptions