Add RecoverySystem shell commands

Allow the reboot escrow commands to be called from ADB shell. This is
needed for CTS host-based tests.

Bug: 143695053
Bug: 63928581
Test: adb shell cmd recovery request-lskf test1
Test: adb shell cmd recovery clear-lskf
Test: adb shell cmd recovery request-lskf test2
      adb shell cmd recovery reboot-and-apply test2
Change-Id: I06c210eff0e4bad9f0c5fe6ec18333d5074816a4