S3 Ignore Subdomain for Bucketname Flag (#1419)

* Some circumstances need subdomains to be ignored rather that interpreted as bucketname, this patch allows such behaviour to be configured

* Adding helper case whereby localstack features as path based exception

* Remove whitespace :(

tests/test_s3/test_s3_utils.py

@@ -1,4 +1,5 @@
 from __future__ import unicode_literals
+import os
 from sure import expect
 from moto.s3.utils import bucket_name_from_url, _VersionedKeyStore, parse_region_from_url
 
@@ -16,6 +17,12 @@ def test_localhost_without_bucket():
     expect(bucket_name_from_url(
         'https://www.localhost:5000/def')).should.equal(None)
 
+def test_force_ignore_subdomain_for_bucketnames():
+    os.environ['S3_IGNORE_SUBDOMAIN_BUCKETNAME'] = '1'
+    expect(bucket_name_from_url('https://subdomain.localhost:5000/abc/resource')).should.equal(None)
+    del(os.environ['S3_IGNORE_SUBDOMAIN_BUCKETNAME'])
+    
+
 
 def test_versioned_key_store():
     d = _VersionedKeyStore()