Fix test script shard bug.

This will help with rollout of TE-720 and any future new shards.

scripts/all-tests.sh

@@ -190,7 +190,7 @@ END
                 # action doesn't fail the build.
                 # May be unnecessary if we changed the "Skip if there are no test files"
                 # option to True in the jenkins job definitions.
-                mkdir -p reports
+                mkdir -p reports/bok_choy
                 cat > reports/bok_choy/xunit.xml <<END
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuite name="nosetests" tests="1" errors="0" failures="0" skip="0">