wendelin: custom test runner to load our own libstdc++

@Tyagov, please review.

Now the test runners use the LD_PRELOAD environment variable to load
the correct libstdc++ built by slapos and restart themselves.

The restart is necessary because LD_PRELOAD is only taken into account
at the time the process is started. Changing this environment variable
in runtime has no effects.

Tests results are available at Nexedi's ERP5 and are 100% ok: https://nexedi.erp5.net/test_result_module/20160927-3FA05624.

/reviewed-on !99

software/wendelin/software.cfg

@@ -12,6 +12,8 @@ parts +=
   ipython
   wendelin.core
   ipython-notebook
+  wendelin_test_suite_runner
+  wendelin_testrunner
 
 [eggs]
 initialization =
@@ -24,7 +26,35 @@ eggs +=
   ${msgpack-python:egg}
   ${wendelin.core:egg}
   ${ipython:egg}
-
+  
+[generic_testrunner_init]
+initialization = 
+  # The 4 lines below will replace the process with another one, with the proper
+  # LD_PRELOAD environment variable. This is necessary because LD_PRELOAD is only
+  # taken into account when the process starts. Modifying it in runtime doesn't
+  # work.
+  import struct, os
+  arch = 8 * struct.calcsize("P")
+  rerun = not os.getenv('LD_PRELOAD')
+  if rerun: os.environ['LD_PRELOAD'] = '''${gcc-fortran:location}/lib%s/libstdc++.so''' % arch
+  if rerun: os.execve(os.path.realpath(__file__), sys.argv, os.environ)
+  
+[wendelin_test_suite_runner]
+<= test_suite_runner
+# we need to override the test suite runner to add our custom libstdc++ dynamic
+# library to the path
+initialization =
+  ${generic_testrunner_init:initialization}
+  ${test_suite_runner:initialization}
+  
+[wendelin_testrunner]
+<= testrunner
+# we need to override the test suite runner to add our custom libstdc++ dynamic
+# library to the path
+initialization =
+  ${generic_testrunner_init:initialization}
+  ${testrunner:initialization}
+ 
 [erp5_repository_list]
 repository_id_list += wendelin