Automatically convert process_input to bytes

On py35, if process_input is a string we end with an Error:
TypeError: memoryview: a bytes-like object is required, not 'str'

A whole lot of code in os-brick/cinder/neutron currently need
to be fixed. Hardest problem is tracking down every instance of
this problem and trying to test/fix it at source. See example
of cinder/os-brick/oslo.rootwrap/oslo.privep code problem here:
http://logs.openstack.org/43/418643/2/check/gate-rally-dsvm-py35-cinder-nv/6efa7b5/logs/screen-n-cpu.txt.gz?level=ERROR

It's just better to fix it in one spot and pass the correct
thing to subprocess.communicate

Change-Id: I88d1510a7ba4c020f73452f0b80e996c22b1edf1

oslo_concurrency/processutils.py

@@ -28,6 +28,7 @@ import sys
 import time
 
 import enum
+from oslo_utils import encodeutils
 from oslo_utils import importutils
 from oslo_utils import strutils
 from oslo_utils import timeutils
@@ -188,7 +189,7 @@ def execute(*cmd, **kwargs):
     :param cwd:             Set the current working directory
     :type cwd:              string
     :param process_input:   Send to opened process.
-    :type process_input:    string
+    :type process_input:    string or bytes
     :param env_variables:   Environment variables and their values that
                             will be set for the process.
     :type env_variables:    dict
@@ -259,6 +260,9 @@ def execute(*cmd, **kwargs):
     process.  If this parameter is used, the child process will be spawned by a
     wrapper process which will set limits before spawning the command.
 
+    .. versionchanged:: 3.17
+       *process_input* can now be either bytes or string on python3.
+
     .. versionchanged:: 3.4
        Added *prlimit* optional parameter.
 
@@ -266,7 +270,7 @@ def execute(*cmd, **kwargs):
        Added *cwd* optional parameter.
 
     .. versionchanged:: 1.9
-       Added *binary* optional parameter. On Python 3, *stdout* and *stdout*
+       Added *binary* optional parameter. On Python 3, *stdout* and *stderr*
        are now returned as Unicode strings by default, or bytes if *binary* is
        true.
 
@@ -279,6 +283,8 @@ def execute(*cmd, **kwargs):
 
     cwd = kwargs.pop('cwd', None)
     process_input = kwargs.pop('process_input', None)
+    if process_input is not None:
+        process_input = encodeutils.to_utf8(process_input)
     env_variables = kwargs.pop('env_variables', None)
     check_exit_code = kwargs.pop('check_exit_code', [0])
     ignore_exit_code = False

oslo_concurrency/tests/unit/test_processutils.py

@@ -236,6 +236,14 @@ exit 1
                                         cwd=tmpdir)
         self.assertIn(tmpdir, out)
 
+    def test_process_input_with_string(self):
+        code = ';'.join(('import sys',
+                         'print(len(sys.stdin.readlines()))'))
+        args = [sys.executable, '-c', code]
+        input = "\n".join(['foo', 'bar', 'baz'])
+        stdout, stderr = processutils.execute(*args, process_input=input)
+        self.assertEqual("3", stdout.rstrip())
+
     def test_check_exit_code_list(self):
         processutils.execute('/usr/bin/env', 'sh', '-c', 'exit 101',
                              check_exit_code=(101, 102))