nut: simplify/improve consistency for RUNAS and STATEPATH

nut: simplify/improve consistency for RUNAS and STATEPATH

We claimed we only supported a single upsd section named 'upsd' and a
single uspmon section named 'upsmon', but when determining RUNAS
and STATEPATH we were using overly-complex functions as we were
attempting to support multiple upsd and upsmon sections.

Simplify the logic by adhering to our stated support.

While were are at it we make RUNAS handling more consistent between
nut-server (upsd) and nut-monitor (upsmon).

We no longer try to limp along if RUNAS is not set by find_runas; to do
this properly would require over-complicated logic when setting file
and directory permissions and ownership.

Signed-off-by: Daniel F. Dickinson <redacted>