Make PyAuto flakiness debugging easier by having PyAuto tests not overwrite NACL_EXE_STDOUT and NACL_EXE_STDERR if they are already set.
Make PyAuto flakiness debugging easier by having PyAuto tests not overwrite
NACL_EXE_STDOUT and NACL_EXE_STDERR if they are already set.

TEST= Set the two environment variables to a file where the
output is to be written. Run, e.g., ./scons run_pyauto_multiple_nexes_test.
The console output from the tests is now in the chosen file.

R= ncbray@google.com
BUG= http://code.google.com/p/nativeclient/issues/detail?id=1818

Review URL: http://codereview.chromium.org/7200016

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@5710 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client