Avocado: add a default encoding setting

And use it when running tests.

Note: this is a partial implementation, to satisfy the following use
case:

   $ echo "#!/bin/sh" > a.sh
   $ echo "echo ěčřž" >> a.sh
   $ chmod +x a.sh
   $ avocado run a.sh
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/core/defaults.py

+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See LICENSE for more details.
+#
+# Copyright: Red Hat Inc. 2018
+# Author: Cleber Rosa <crosa@redhat.com>
+
+"""
+The Avocado core defaults
+"""
+
+#: The encoding used by default on all data input
+ENCODING = 'utf-8'

avocado/core/test.py

@@ -32,6 +32,7 @@ from difflib import unified_diff
 from six import string_types, iteritems
 
 from . import data_dir
+from . import defaults
 from . import exceptions
 from . import output
 from . import parameters
@@ -1133,7 +1134,7 @@ class SimpleTest(Test):
 
             # process.run uses shlex.split(), the self.path needs to be escaped
             result = process.run(self._command, verbose=True,
-                                 env=test_params)
+                                 env=test_params, encoding=defaults.ENCODING)
 
             self._log_detailed_cmd_info(result)
         except process.CmdError as details: