Set the default executor count for a dumb slave to 1, so the user is not forced to type this in.

core/src/main/resources/hudson/slaves/DumbSlave/configure-entries.jelly

@@ -33,7 +33,7 @@ THE SOFTWARE.
   </f:entry>
 
   <f:entry title="${%# of executors}" field="numExecutors">
-    <f:number clazz="positive-number" min="1" step="1" />
+    <f:number clazz="positive-number" min="1" step="1" default="1"/>
   </f:entry>
 
   <f:entry title="${%Remote FS root}" field="remoteFS">
@@ -88,4 +88,4 @@ THE SOFTWARE.
 
   <f:descriptorList title="${%Node Properties}" descriptors="${h.getNodePropertyDescriptors(descriptor.clazz)}" field="nodeProperties" />
   
-</j:jelly>
\ No newline at end of file
+</j:jelly>