Replace toolset=x,y with toolset=x toolset=y in bjam invocations to allow --toolsets=gcc/cxxstd=03,gcc/cxxstd=11 to work

Author: pdimov

testing/src/regression.py

@@ -772,8 +772,8 @@ def bjam_cmd( self, toolsets, args = '', *rest ):
             'arg' : args }
 
         if toolsets:
-            import string
-            cmd += ' toolset=' + toolsets
+            for toolset in toolsets.split( ',' ):
+                cmd += ' toolset=' + toolset
 
         return cmd