bug 1159337 - Debug occasional test failure
bug 1159337 - Debug occasional test failure

When the test test_post_add_second_subfeature results in an unexpected
feature order, print a bunch of debug data, including the MPTT state and
database queries, before failing the test. This debug code does not run
under normal API calls, only in the test.

renoirb/browsercompat,renoirb/browsercompat,jwhitlock/web-platform-compat,mdn/browsercompat,jwhitlock/web-platform-compat,renoirb/browsercompat,jwhitlock/web-platform-compat,mdn/browsercompat,mdn/browsercompat