Fix "adb shell cmd user" output.

Print out help message if user command is empty, "help" or "-h".
Print out "Unknown command" if user command is not supported.

Fix: 34320186
Test: mmm -j20 frameworks/base/
Change-Id: I9f0fcf56f546e4a4f40a57f713b826d96de8ac09
1 file changed