Update platform command and test for Python 2 & 3

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

mayan/apps/platform/management/commands/platformtemplate.py

@@ -40,8 +40,11 @@ class Command(management.BaseCommand):
                 )
                 exit(1)
             else:
+                # Python 2 & 3 way to convert from SafeString to unicode
                 self.stdout.write(
+                    '{}'.format(
                         template().render(
                             context_string=options.get('context')
                         )
                     )
+                )

mayan/apps/platform/tests/test_management_commands.py

@@ -1,6 +1,6 @@
 from __future__ import unicode_literals
 
-from io import BytesIO
+from django.utils.six import StringIO
 
 from django.core import management
 from django.test import TestCase
@@ -38,7 +38,7 @@ PlatformTemplate.register(klass=TestPlatformTemplate)
 class PlatformTemplateManagementCommandTestCase(TestCase):
 
     def test_platform_template_simple(self):
-        output = BytesIO()
+        output = StringIO()
         args = (TEST_TEMPLATE_NAME,)
         options = {
             'stdout': output
@@ -47,7 +47,7 @@ class PlatformTemplateManagementCommandTestCase(TestCase):
         self.assertEqual(output.getvalue(), TEST_TEMPLATE_STRING_RENDER)
 
     def test_platform_template_context(self):
-        output = BytesIO()
+        output = StringIO()
         args = (
             TEST_TEMPLATE_NAME, '--context',
             'test_template_variable: {}'.format(