Description of the problem / feature request:

Tooling for coverage fails when running under remote execution (LcovMerger specifically)

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Run a test target with bazel coverage --spawn_strategy=remote --remote_executor=... //path/to:test

What operating system are you running Bazel on?

Ubuntu 14.04

What's the output of bazel info release?

release 0.10.1

Any other information, logs, or outputs that you want to share?

Relevant portion of coverage execution

+ exec bazel-out/k8-fastbuild/bin/external/bazel_tools/tools/test/LcovMerger --coverage_dir=%execroot%/_coverage/path/to/test/test --output_file=%execroot%/bazel-out/k8-fastbuild/testlogs/path/to/test/coverage.dat
%execroot%/bazel-out/k8-fastbuild/bin/external/bazel_tools/tools/test/LcovMerger: Cannot locate runfiles directory. (Set $JAVA_RUNFILES to inhibit searching.)