builders/scheduler: Add ability to select the worker to run on

Thanks to tardyp for the pointer to an example of how to make this work!

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

builders.py

@@ -7,6 +7,7 @@ from datetime import datetime
 
 import os
 import json
+import random
 
 
 builders = []
@@ -189,6 +190,14 @@ def create_builder_factory():
         timeout=16200))  # default of 1200s/20min is too short, use 4.5hrs
     return f
 
+def nextWorker(bldr, workers, buildrequest):
+    forced_worker = buildrequest.properties.getProperty("worker", "*")
+    if forced_worker == "*":
+        return random.choice(workers) if workers else None
+    for w in workers:
+        if w.worker.workername == forced_worker:
+            return w
+    return None  # worker not yet available
 
 # regular builders
 f = create_builder_factory()
@@ -197,7 +206,7 @@ for builder in config.subbuilders:
     if not workers:
         workers = config.builder_to_workers['default']
     builders.append(util.BuilderConfig(name=builder,
-                                       workernames=workers,
+                                       workernames=workers, nextWorker=nextWorker, 
                                        factory=f, env=extra_env))
 
 def create_parent_builder_factory(buildername, waitname):

schedulers.py

@@ -74,8 +74,14 @@ def props_for_builder(builder):
             label="Do we want to deploy artefacts? ",
             default=False
         ))
-
     props = props + repos_for_builder(builder)
+    worker_list = config.builder_to_workers.get(builder, config.builder_to_workers['default'])
+    props.append(util.ChoiceStringParameter(name="worker",
+                              label="Worker to run the build on",
+                              default="*",
+                              multiple=False,
+                              strict=True,
+                              choices=worker_list))
     return props