Improve debuggability of a few sanitizer tests

[alexcrichton]

Investigating failures on Travis...

[rust-highfive]

r? @nikomatsakis

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[alexcrichton]

cc @kennytm

Last successful auto build: https://travis-ci.org/rust-lang/rust/jobs/272889516
First failed auto build: https://travis-ci.org/rust-lang/rust/jobs/273020652

Note that the kernel changed between those two builds. My guess is Travis deployed an update and it broke us. No response on their slack channel yet, hoping this can help investigate.

[kennytm]

Should we just wait for the 4.4.0-94 kernel (assuming the update will fix the bug mentioned in google/sanitizers#856 (comment)) + Travis cookbook update, and then revert #44399?

[alexcrichton]

Since this works I think I'll land this, that way we don't have to rely on Travis keeping support for an older kernel. I'll comment this, clean it up, and resubmit.