[XRay][compiler-rt][NFC] Clean up xray log files before running test
[XRay][compiler-rt][NFC] Clean up xray log files before running test

Improves the test behaviour in the face of failure. Without this change
the fdr-single-thread.cc test may leave around artefacts of a previous
failing run since the cleanup doesn't happen if any of the intermediary
steps fail.

Non-functional change.

Subscribers: llvm-commits

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@316548 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt