Bug 1274980 part 1: Add support for test platform regex match. r=dustin

Often we need to setup a test configuration for different platforms, but
not for different platform builds (opt/debug). This leads to cumbersome
configuration duplicates. This patch adds support for platform regular
expression matching. For example, if you want to configure the chunk
size for linux64 platform both for opt and debug, originally you would
do this:

chunks:
    by-test-platform:
        linux64/opt: 4
        linux64/debug: 4
        default: 8

With regular expression matching, you only need:

chunks:
    by-test-platform:
        linux64/.*: 4
        default: 8

This patch was originally written by Geoffrey Brown for Windows support.

MozReview-Commit-ID: HFP52N9Ef0k

--HG--
extra : rebase_source : d2a5129b7459fc7f71f59da76d45526cef028e44

taskcluster/taskgraph/test/test_transforms_base.py

@@ -81,6 +81,20 @@ class TestKeyedBy(unittest.TestCase):
         }
         self.assertEqual(get_keyed_by(test, 'option', 'x'), 20)
 
+    def test_by_value_regex(self):
+        test = {
+            'test-name': 'tname',
+            'option': {
+                'by-test-platform': {
+                    'macosx64/.*': 10,
+                    'linux64/debug': 20,
+                    'default': 5,
+                },
+            },
+            'test-platform': 'macosx64/debug',
+        }
+        self.assertEqual(get_keyed_by(test, 'option', 'x'), 10)
+
     def test_by_value_default(self):
         test = {
             'test-name': 'tname',