Floss: implement restricted mode in btclient

Implement the following command options:
  --restricted		disallow toggling adapter power when set
  --command <COMMAND>	execute the command without entering the shell

Bug: 239432313
Test: deploy and run
1. btclient; (in shell) adapter disable
2. btclient --restricted; (in shell) adapter disable
3. btclient --command "adapter disable"
4. btclient --restricted --command "adapter disable"
Verified 1 and 3 success. 2 and 4 fail.
Tag: #floss

Change-Id: Ied236ce3f336ae89847de28b000e21ccd58eeb0b