working proof of concept for num_cpus.cpus=X

reprotest/build.py

@@ -333,19 +333,21 @@ def aslr(ctx, build, vary):
 
 def num_cpus(ctx, build, vary):
     _ = build
-    if ctx.num_cpus.cpus:
+    if not vary:
+        _ = _.append_setup_exec_raw('CPU_MAX=$(nproc)')
+    elif not ctx.spec.num_cpus.cpus:
         _ = _.append_setup_exec_raw('CPU_MAX=$(nproc)')
     else:
-        _ = _.append_setup_exec_raw('CPU_MAX=%s' % ctx.num_cpus.cpus)
+        _ = _.append_setup_exec_raw('CPU_MAX=%s' % random.choice(ctx.spec.num_cpus.cpus))
     _ = _.append_setup_exec_raw('CPU_MIN=$({ echo $CPU_MAX; echo %s; } | sort -n | head -n1)' % ctx.min_cpus)
     if ctx.min_cpus <= 0:
         raise ValueError("--min-cpus must be a positive integer: " % ctx.min_cpus)
     if not vary:
         _ = _.append_setup_exec_raw('CPU_NUM=$CPU_MIN')
-    if ctx.num_cpus.cpus:
+    elif ctx.spec.num_cpus.cpus:
         _ = _.append_setup_exec_raw('CPU_NUM=$(if [ $CPU_MIN = $CPU_MAX ]; \
             then echo $CPU_MIN; echo >&2 "only 1 CPU is available; num_cpus is ineffective"; \
-            else echo %s; fi)' % ctx.num_cpus.cpus)
+            else echo %s; fi)' % random.choice(ctx.spec.num_cpus.cpus))
     else:
         # random number between min_cpus and $(nproc)
         _ = _.append_setup_exec_raw('CPU_NUM=$(if [ $CPU_MIN = $CPU_MAX ]; \
@@ -589,10 +591,10 @@ class LocalesVariation(collections.namedtuple('_LocaleVariation', 'locale')):
     def default(cls):
         return cls(mdiffconf.strlist_set(";"))
 
-class NumCpusVariation(collections.namedtuple('_LocaleVariation', 'cpus')):
+class NumCpusVariation(collections.namedtuple('_NumCpusVariation', 'cpus')):
     @classmethod
     def default(cls):
-        return None
+        return cls(mdiffconf.strlist_set(";"))
 
 class VariationSpec(mdiffconf.ImmutableNamespace):
     @classmethod