Add master_manager_launch script which launches master_manager scripts for each master on a host.

infra/libs/buildbot/test/master_test.py

Index: infra/libs/buildbot/test/master_test.py
diff --git a/infra/libs/buildbot/test/master_test.py b/infra/libs/buildbot/test/master_test.py
index 32140807396d89b2b7574e74075d2b0b425324af..87b63b9734a32f83d87618152c0edb277a98b097 100644
--- a/infra/libs/buildbot/test/master_test.py
+++ b/infra/libs/buildbot/test/master_test.py
@@ -155,6 +155,18 @@ class TestMasterInformation(auto_stub.TestCase):
     self.mock(requests, 'get', timeout)
     self.assertIsNone(master.get_accepting_builds(self.chromium_fyi))
 
+  def testMastermapHost(self):
+    masters = [
+        {'fullhost': 'bananas.cool'},
+        {'fullhost': 'bananas.cool'},
+        {'fullhost': 'bananas_dos.cool'},
+    ]
+    self.mock(master, '_call_mastermap', lambda _x: masters)
+
+    self.assertEqual(
+        len(master.get_mastermap_for_host('fake', 'bananas.cool')),
+        2)
+
 class TestMasterManipulation(auto_stub.TestCase):
   def setUp(self):
     super(TestMasterManipulation, self).setUp()