libbinder: require shell/root UID for shell

The APIs under SHELL_COMMAND_TRANSACTION are considered to be
development APIs and are not suitable for actual usage on the device,
especially where the APIs need to be stable over long periods of
time.

Bug: N/A

Test: as follows
walleye:/ # su root cmd package list packages
<successful output>
walleye:/ # su shell cmd package list packages
<successful output>
walleye:/ # su system cmd package list packages
cmd: Failure calling service package: Operation not permitted (1)

Change-Id: I236281ba0346711f89507d026eadd5ae3c9337b1