This reverts commit 0c629b21.

This was not the way of upgrading the package in chrombrew build.

See also slapos!720

 * correctly test if shill was launched with our wrapper
 * writing accept_ra sys parameter with "all" interface doesn't work
 * no need to remove default routes as writing forwarding sys parameter already does it
 * killall doesn't exist on NayuOS

The shill network manager in Chrom*OS automatically overwrites the Accept Router Advertisements preference to default even if forwarding.
Since Re6st machines act as routers, we do not want this to happen, hence Grandenet wil set it to Accept.
To avoid a race condition, however, we redirect all file write to the approrpriate preference file to go to /dev/null.
Adapted by https://lab.nexedi.com/nexedi/userhosts/

Set proper destination for python and openssl
Add configuration options for some packages that do not compile
Remove superfluous rebootstrap extension