[Telemetry] Add timeout to telemetry run_tests

tools/telemetry/third_party/subprocess32/testdata/sigchild_ignore.py

+import signal, subprocess32, sys, time
+# On Linux this causes os.waitpid to fail with OSError as the OS has already
+# reaped our child process.  The wait() passing the OSError on to the caller
+# and causing us to exit with an error is what we are testing against.
+sig_child = getattr(signal, 'SIGCLD', None)
+if sig_child is None:
+    sig_child = getattr(signal, 'SIGCHLD')
+signal.signal(sig_child, signal.SIG_IGN)
+subprocess32.Popen([sys.executable, '-c', 'print("albatross")']).wait()
+# Also ensure poll() handles an errno.ECHILD appropriately.
+p = subprocess32.Popen([sys.executable, '-c', 'print("albatross")'])
+num_polls = 0
+while p.poll() is None:
+    # Waiting for the process to finish.
+    time.sleep(0.01)  # Avoid being a CPU busy loop.
+    num_polls += 1
+    if num_polls > 3000:
+        raise RuntimeError('poll should have returned 0 within 30 seconds')