Rollup merge of #43536 - alexcrichton:privileged, r=TimNN

Flag docker invocations as --privileged on CI

When upgrading to LLVM 5.0 it was found that the leak sanitizer tests were
failing with fatal errors, but they were passing locally when run. Turns out it
looks like they may be using new ptrace-like syscalls so the docker container
now needs `--privileged` when executing to complete the test.