Add Winscope report to the bugreport when using continuous mode

When logging window traces in continuous mode the window manager doesn't
continuously save data to disk.

The window traces (continuous or not) have to be present in the bug
report.

Add instruction to dump the window trace during bugreporting.

To activate continuous trace:
- adb shell cmd window tracing continuous true
- adb shell cmd window tracing start

To manually dump window trace:
 - adb shell dumpsys window trace

Test: Flash a device. Set continuous mode. Start the trace. Trigger a
bugreport. Check if the zip file contains the a wm_trace.pb under
FS/data/misc/wmtrace

Change-Id: I1af0b3b37e48ba026fa64515d7e330a2ba7663b6