Make merging of shard test results handle test suites that are split across shards better.

tools/sharding_supervisor/data/gtest_results_expected.xml

Index: tools/sharding_supervisor/data/gtest_results_expected.xml
diff --git a/tools/sharding_supervisor/data/gtest_results_expected.xml b/tools/sharding_supervisor/data/gtest_results_expected.xml
new file mode 100644
index 0000000000000000000000000000000000000000..7af04d4cbe57e920ddeb673c7564276d27cadbcc
--- /dev/null
+++ b/tools/sharding_supervisor/data/gtest_results_expected.xml
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<testsuites name="AllTests" tests="" failures="" disabled="" errors="" time="">
+  <!-- See comments in gtest_results.xml0 for what the different suites represent -->
+  <testsuite name="Suite0" tests="1" failures="" disabled="" errors="" time="">
+    <testcase name="Test0" status="run" time="0" classname="Suite0" />
+  </testsuite>
+  <testsuite name="Suite1" tests="1" failures="" disabled="" errors="" time="">
+    <testcase name="Test0" status="run" time="1" classname="Suite1">
+      <failure message="" type="" ignored="true"></failure>
+    </testcase>
+  </testsuite>
+  <testsuite name="Suite2" tests="2" failures="" disabled="" errors="" time="">
+    <testcase name="Test0" status="run" time="0" classname="Suite2" />
+    <testcase name="Test1" status="run" time="0" classname="Suite2" />
+  </testsuite>
+  <testsuite name="Suite3" tests="1" failures="" disabled="" errors="" time="">
+    <testcase name="Test0" status="run" time="0" classname="Suite3">
+      <failure message="" type="" ignored="true"></failure>
+      <failure message="" type="" ignored="true"></failure>
+    </testcase>
+  </testsuite>
+</testsuites>