simpleperf: fix app_profiler.py.

Previous change makes app_profiler.py not work on rooted devices
because of using '>xxx' as a flag to store stdout files. Change
this to a more obvious way.

Bug: http://b/62028152
Test: run app_profiler.py on both rooted and non-rooted devices.
Change-Id: Ice2399d007a64a7d0000560b2368a392620b1053
2 files changed