Fix --enable-valgrind-daemon option.

Don't add the "valgrind channel" to the appliance.

Just dump out the valgrind.log to stderr while the daemon is running.

Ensure that if valgrind tests fail in the appliance, that we don't
exit with success in the library by checking for a canary message in
the verbose daemon logs.

This allows the option to be used routinely by developers.
daemon: Remove unnecessary sysroot_path (selinux).

This fixes commit 72afcf450a78b7e58f65b4a7aaf94d71cd25fca5.