Write tests to discover smidump files with invalid content

[lunkwill42]

Sometimes, humans (and even machines) make mistakes, and the Python modules produced by the smidump program contain invalid data. E.g. if the MIB module being dumped depends on other modules that aren't available to smidump, it might produce a full dump that contains incomplete OIDs, such as was the case in #2494.

We should have at least one test generator that produces a test for every smidump module in NAV and test all the OIDs in that file for validity.

The issue with #2494 was that the OID's lacked a proper prefix, causing them all to start with 0.. The NET-SNMP library (underlying pynetsnmp-2) refused to build ASN.1 representations of these OIDs, so somehow utilizing NET-SNMP to verify valid OIDs would be prudent.

Originally posted by @lunkwill42 in #2494 (comment)