Fix adb bugreport and add bugreport unit tests.

Commit 58d72e22 introduced a regression, which made fullbugreport as the
default mode. This lead to 'adb bugreport SAMPLE_BR' triggering a
progress notification on the device as it inherited do_broadcast from full bugreport.

Fix the issue by separating full bugreport from default bugreport.

Add unit tests for all the cases of calling bugreport.

Bug: 119877616
Test: Verified that 'adb bugreport SAMPLE_BR' does not show any notification on the device.
Test: mmm -j frameworks/native/cmds/dumpstate/ && adb push ${OUT}/data/nativetest64/dumpstate_test* /data/nativetest64 && adb shell /data/nativetest64/dumpstate_test/dumpstate_test && printf "\n\n#### ALL TESTS PASSED ####\n"

Change-Id: I06e57454a91a3276dd89d47b3b0a04d3d85f32da