nut-scanner fails due to simulation mode if CONFPATH does not exist

[jimklimov]

Fall-out from #2246 / #2242 :

   0.175520     [D1] nutscan_init: succeeded to load the library for NUT Client library
   0.175529     Scanning USB bus.
   0.175577     No start IP, skipping SNMP
   0.175580     Scanning XML/HTTP bus.
   0.175583     [D1] XML/HTTP SCAN: starting pthread_create with run_xml...
   0.175605     [D1] run_usb: using library default link_detail_level settings
   0.175623     No start IP, skipping NUT bus (old connect method)
   0.175627     Scanning NUT simulation devices.
   0.175629     [D1] NUT simulation devices SCAN: starting pthread_create with run_nut_simulation...
   0.175674     Scanning NUT bus (avahi method).
   0.175678     [D1] NUT bus (avahi) SCAN: starting pthread_create with run_avahi...
   0.175677     [D1] Scanning XML/HTTP bus using broadcast.
   0.175714     [D2] nutscan_scan_xml_http_generic() : scanning connected network segment(s) with a broadcast, attempt 1 of 3 with a timeout of 5000000 usec
   0.175724     Scanning IPMI bus.
   0.175728     [D1] IPMI SCAN: starting pthread_create with run_ipmi...
   0.175723     [D1] Scanning: /usr/local/ups/etc
   0.175749     Failed to open /usr/local/ups/etc: No such file or directory
   0.175873     [D5] nutscan_scan_xml_http_generic() : sent request to <broadcast>, loop #1/3, waiting for responses
nut$

Probably related to fatal_with_errno() below:

    upsdebugx(1, "Scanning: %s", CONFPATH);

    if ((dp = opendir(CONFPATH)) == NULL) {
        fatal_with_errno(EXIT_FAILURE, "Failed to open %s", CONFPATH);
        return NULL;
    }

[jimklimov]

Addressed by commit cd4e190 (issue link in comment botched)