Ignore a test which is blocking a snapshot

@catamorphism says he has a fix coming soon, so I didn't allocate an issue for
it. If it festers for more than a few days I'll open something up though.
auto merge of #9269 : alexcrichton/rust/ignore-rustpkg-test, r=brson

@catamorphism says he has a fix coming soon, so I didn't allocate an issue for
it. If it festers for more than a few days I'll open something up though.