telemetry: Robustify CrOSInterface._GetSessionManagerPid().

Allow the session_manager process name to use a relative
path or to not have any arguments, rather than requiring it
to have the prefix "/sbin/session_manager " (note trailing
space).

BUG=377301

Review URL: https://codereview.chromium.org/302163004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274225 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/backends/chrome/cros_interface.py

@@ -297,7 +297,8 @@ class CrOSInterface(object):
     """Returns the pid of the session_manager process, given the list of
     processes."""
     for pid, process, _, _ in procs:
-      if process.startswith('/sbin/session_manager '):
+      argv = process.split()
+      if argv and os.path.basename(argv[0]) == 'session_manager':
         return pid
     return None