Update so that the content types searched for launch-index

variable has a little more meaning and by default look in
metadata for 'launch-index' and have ec2 instead look for 
a different variable (thus allowing more datasources to just work).

cloudinit/cloud.py

@@ -76,8 +76,9 @@ class Cloud(object):
     def get_instance_id(self):
         return self.datasource.get_instance_id()
 
-    def get_launch_index(self):
-        return self.datasource.get_launch_index()
+    @property
+    def launch_index(self):
+        return self.datasource.launch_index
 
     def get_public_ssh_keys(self):
         return self.datasource.get_public_ssh_keys()

cloudinit/sources/DataSourceEc2.py

@@ -77,7 +77,10 @@ class DataSourceEc2(sources.DataSource):
                         self.metadata_address)
             return False
 
-    def get_launch_index(self):
+    @property
+    def launch_index(self):
+        if not self.metadata:
+            return None
         return self.metadata.get('ami-launch-index')
 
     def get_instance_id(self):

cloudinit/sources/__init__.py

@@ -68,13 +68,18 @@ class DataSource(object):
             return self._filter_userdata(self.userdata)
         return self.userdata
 
-    def get_launch_index(self):
+    @property
+    def launch_index(self):
+        if not self.metadata:
+            return None
+        if 'launch-index' in self.metadata:
+            return self.metadata['launch-index']
         return None
 
     def _filter_userdata(self, processed_ud):
         if not processed_ud:
             return processed_ud
-        idx = self.get_launch_index()
+        idx = self.launch_index
         if idx is None:
             return processed_ud
         # First do a scan to see if any one with launch-index

cloudinit/user_data.py

@@ -53,7 +53,8 @@ ARCHIVE_UNDEF_TYPE = "text/cloud-config"
 ATTACHMENT_FIELD = 'Number-Attachments'
 
 # Only the following content types can have there launch index examined
-CAN_HAVE_LAUNCH_INDEX = ["text/cloud-config", "text/cloud-config-archive"]
+# in there payload, evey other content type can still provide a header
+EXAMINE_FOR_LAUNCH_INDEX = ["text/cloud-config", "text/cloud-config-archive"]
 
 
 class UserDataProcessor(object):
@@ -101,7 +102,7 @@ class UserDataProcessor(object):
     def _attach_launch_index(self, msg):
         header_idx = msg.get('Launch-Index', None)
         payload_idx = None
-        if msg.get_content_type() in CAN_HAVE_LAUNCH_INDEX:
+        if msg.get_content_type() in EXAMINE_FOR_LAUNCH_INDEX:
             try:
                 # See if it has a launch-index field
                 # that might affect the final header