Generate stable targets rather than random

A random value can still easily hit collision, and at least
one was found easily on the gates (gone with a recheck).
Moreover, the usage of a random target does not allow for ensuring
reproducible builds: the usage of an hash build from the node
content makes sure that the target is stable across different
runs of api-ref generation.

Change-Id: I3fcd8a4e5b0a66c9dbf34f4a4c472f3c93c46bb8

os_api_ref/__init__.py

@@ -11,8 +11,8 @@
 # under the License.
 
 from collections import OrderedDict
+import hashlib
 import os
-import random
 import re
 
 from docutils import nodes
@@ -199,8 +199,11 @@ class RestMethodDirective(rst.Directive):
 
         # We need to build a temporary target that we can replace
         # later in the processing to get the TOC to resolve correctly.
-        temp_target = "%s-%d-selector" % (node['target'],
-                                          random.randint(1, 1000))
+        # SHA-1 is used even if collisions are possible, because
+        # they are still unlikely to occurr and it is way shorter
+        # than stronger SHAs.
+        node_hash = hashlib.sha1(str(node).encode('utf-8')).hexdigest()
+        temp_target = "%s-%s-selector" % (node['target'], node_hash)
         target = nodes.target(ids=[temp_target])
         self.state.add_target(temp_target, '', target, lineno)
         section += node