Add decorations to bot names for modifying parts of try sets.

scripts/master/try_job_base_bb7.py

Index: scripts/master/try_job_base_bb7.py
===================================================================
--- scripts/master/try_job_base_bb7.py	(revision 113400)
+++ scripts/master/try_job_base_bb7.py	(working copy)
@@ -12,6 +12,7 @@
 from twisted.web import http
 
 from master.try_job_stamp import TryJobStamp
+import master.try_job_decoration as decor
 
 
 class TryJobBaseMixIn:
@@ -106,11 +107,12 @@
     build_sets = []
     for builder_name in builder_names:
       build_set = buildset.BuildSet(
-          [builder_name],
+          builder_name.split(':')[0:1],
           jobstamp,
           reason=reason,
           bsid=buildset_id,
-          properties=props)
+          properties=decor.parse_decoration(props,
+              ':'.join(builder_name.split(':')[1:])))
       build_sets.append(build_set)
       self.CancelJobsMatching(build_set, builder_name)
     for build_set in build_sets: