Enable New Style class check

* update pants.ini to enable new style class checks
* cleanup problems in existing code base.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/80334805

Bugs closed: 1905, 2194

Reviewed at https://rbcommons.com/s/twitter/r/2820/

pants.ini

@@ -116,7 +116,7 @@ skip: True
 skip: True
 
 [pycheck-newstyle-classes]
-skip: True
+skip: False
 
 [pycheck-context-manager]
 skip: True

src/python/pants/reporting/invalidation_report.py

@@ -10,10 +10,10 @@
 from pants.base.target import Target
 
 
-class InvalidationReport:
+class InvalidationReport(object):
   """Creates a report of all versioned target sets seen in the build."""
 
-  class TaskReport:
+  class TaskReport(object):
     class TaskEntry(namedtuple('TaskEntry', ['targets_hash', 'target_ids', 'cache_key_id',
                                              'cache_key_hash', 'phase', 'valid'])):
       """

src/python/pants/scm/git.py

@@ -363,19 +363,19 @@ def isdir(self, relpath):
       return path.endswith('/')
     return False
 
-  class Symlink:
+  class Symlink(object):
 
     def __init__(self, name, sha):
       self.name = name
       self.sha = sha
 
-  class Dir:
+  class Dir(object):
 
     def __init__(self, name, sha):
       self.name = name
       self.sha = sha
 
-  class File:
+  class File(object):
 
     def __init__(self, name, sha):
       self.name = name

tests/python/pants_test/backend/codegen/tasks/test_protobuf_gen.py

@@ -308,7 +308,7 @@ def test_calculate_sources_with_source_root(self):
     self.assertEquals(1, len(result.keys()))
     self.assertEquals(OrderedSet(['project/src/main/proto/proto-lib/foo.proto']), result['project/src/main/proto'])
 
-  class MockLogger:
+  class MockLogger(object):
 
     def __init__(self):
       self._warn = []

tests/python/pants_test/tasks/test_jar_publish.py

@@ -259,7 +259,7 @@ def test_publish_classifiers(self):
     self.assertEquals(r, c)
 
 
-class FailNTimes:
+class FailNTimes(object):
 
   def __init__(self, tries, exc_type, success=None):
     self.tries = tries