dumpstate: Emit a logcat message at beginning and end of execution.

Since the logcat is not printed until later in the output, this will
make it easier to determine at what point the user pressed the key sequence
to initiate the bugreport, which can be helpful when debugging timing dependent problems.

b/2164183

Change-Id: I5b650a6163c383183ff28e344dac36fab11a2c7b
Signed-off-by: Mike Lockwood <lockwood@android.com>