Reset access to system properties on reinitialization

Treat subsequent calls to __system_properties_init() as a
reinitialization of system properties and revoke access to prop files
that have been previously mapped but that the process's current context
does not have access to.  Additionally reset the no_access_ flag in
case permissions have loosened and previously unaccessible files can now
be accessed.

This is meant to work around an issue that setcon() does not revoke
mmap() mappings, so we must manually revoke them after a successful
setcon() call.

Bug 26114086

Change-Id: I4d690abb6817283ca64ac26ea4c1dad398a98fbc