toolbox: add setprop, start, and stop

Move these from toybox as they're Android specific and more easily
maintained here.

A few changes during the conversion:
* Report error in setprop if value is not a UTF8 string; this would
  previously fail only after attempting to set the property
* Inform users to check dmesg for further failure messages for all
  three programs
* Only start/stop zygote_secondary if the device is not single arch

Bug: 117321744
Bug: 133901248
Test: setprop works, start and stop work on single and multi-arch.

Change-Id: Id2194cf2b65221bde38aff91f0e86b33edb37f42