libs/utils/android: Add systrace configuration

Created by: valschneider

For workloads with collect='systrace', systrace can now be configured in a similar manner to ftrace. Simply add a systrace dict in the TestEnv conf like so:

"systrace" : { "events" : [ "gfx", "view", "sched", "freq", "idle" ], "buffsize" : 100 * 1024 }