Disable jvm-platform-analysis by default

Disable by default until it is a bit snappier.

Filed pantsbuild#1972

Testing Done:
pantsbuild#1971

Reviewed at https://rbcommons.com/s/twitter/r/2618/

src/python/pants/backend/jvm/tasks/jvm_platform_analysis.py

@@ -73,7 +73,8 @@ def product_types(cls):
   @classmethod
   def register_options(cls, register):
     super(JvmPlatformValidate, cls).register_options(register)
-    register('--check', default='fatal', choices=['off', 'warn', 'fatal'],
+    # TODO: disabled by default: see https://github.com/pantsbuild/pants/issues/1972
+    register('--check', default='off', choices=['off', 'warn', 'fatal'],
              help='Check to make sure no jvm targets target an earlier jdk than their dependencies')
     register('--children-before-parents', default=False, action='store_true',
              help='Organize output in the form target -> dependencies, rather than '