init: Replace property_set() with android::base::SetProperty()

Init is no longer a special case and talks to property service just
like every other client, therefore move it away from property_set()
and to android::base::SetProperty().

In doing so, this change moves the initial property set up from the
kernel command line and property files directly into PropertyInit().
This makes the responsibilities between init and property services
more clear.

Test: boot, unit test cases
Change-Id: I36b8c83e845d887f1b203355c2391ec123c3d05f