We use computer identifier in fluentd forwarding. This identifier was named as
ors-id, but it applies not only to ORS, but also to generic deployment with
BBU.

In the next patch we are going to introduce ORS mode and move ORS-specific
bits to software-ors.cfg and instance-ors.cfg + co. The computer identifier
will stay in generic part, because it is generic.

-> To avoid ambiguity rename it to be clearly unrelated to ORS specifics.

/cc @jhuge, @lu.xu, @tomo, @xavier_thompson, @Daetalus
/proposed-for-review-on nexedi/slapos!1522
/reviewed-by TrustMe