Fix eunit_surefire crash with rebar eunit tests=...

This fixes the following crash:

> =ERROR REPORT==== 20-Jun-2014::16:35:38 ===
> Error in process <0.40.0> with exit value: {function_clause,[{eunit_surefire,escape_suitename,[undefined,[]],[{file,"eunit_surefire.erl"},{line,416}]},{eunit_surefire,write_report,2,[{file,"eunit_surefire.erl"},{line,258}]},{lists,foreach,2,[{file,"lists.erl"},{line,1336}]},{...
diff --git a/src/rebar_eunit.erl b/src/rebar_eunit.erl
index f1e2ac3..6026740 100644
--- a/src/rebar_eunit.erl
+++ b/src/rebar_eunit.erl
@@ -461,7 +461,7 @@
                             %% Generator
                             MakePrimitive(generator, M, F2)
                     end,
-                [NewFunction|Acc]
+                [eunit_module_suite(M, NewFunction)|Acc]
         end,
     lists:foldl(F, [], RawTests).
 
@@ -473,6 +473,11 @@
 pre15b02_eunit_primitive(generator, M, F) ->
     {generator, eunit_test:function_wrapper(M, F)}.
 
+% Add a test group for eunit_surefire to be able to deduce the testsuite.
+% Calling eunit:test({module, M}) does exactly this as well.
+eunit_module_suite(M, X) ->
+    {"module '" ++ atom_to_list(M) ++ "'", X}.
+
 %%
 %% == run tests ==
 %%