nut-scanner: report bogus and duplicate serial numbers

[jimklimov]

Closes: #1810

UPDATE: Currently addresses sanity-checking for one media type (e.g. SNMP and USB separately), not across multiple discoveries (follow-up in #1813)

Example sanity-checked suggested configuration:

[nutdev1]
        driver = "usbhid-ups"
        port = "auto"
        vendorid = "0463"
        productid = "FFFF"
        product = "Ellipse ECO"
        serial = "000000000"
        vendor = "EATON"
        bus = "003"
        device = "002"
        ###NOTMATCHED-YET###bcdDevice = "0100"

# WARNING: all-same character "serial" with 9 copies of '0' (0x30) reported in some devices: nutdev1

...same with logs bumped:

  15.048347     [D1] SCANS DONE: display results: USB
  15.048351     [D2] nutscan_display_ups_conf_with_sanity_check: USB
  15.048369     [D2] nutscan_display_ups_conf: USB
[nutdev1]
        driver = "usbhid-ups"
        port = "auto"
        vendorid = "0463"
        productid = "FFFF"
        product = "Ellipse ECO"
        serial = "000000000"
        vendor = "EATON"
        bus = "003"
        device = "002"
        ###NOTMATCHED-YET###bcdDevice = "0100"
  15.048398     [D2] nutscan_display_sanity_check: USB
  15.048403     [D2] nutscan_display_sanity_check_serial: USB
  15.048408     [D3] nutscan_display_sanity_check_serial: checking serial numbers for 1 device configuration(s)
  15.048412     [D3] nutscan_display_sanity_check_serial: new entry for serial '000000000'

# WARNING: all-same character "serial" with 9 copies of '0' (0x30) reported in some devices: nutdev2
  15.048419     [D1] SCANS DONE: free resources: USB

[AppVeyorBot]

❌ Build nut 2.8.0.327-master failed (commit 245bee55e8 by @jimklimov)

[AppVeyorBot]

✅ Build nut 2.8.0.328-master completed (commit 858e2ed72c by @jimklimov)