yaml os discovery now respects the os mib_dir definition
mib_dir now only allows strings, not arrays
changed schema validation to account for that
consolidated dell mibs, no reason for them to be spread out
* New OS: QTECH
https://www.qtech.ru/en/catalog/
* QTECH: Add hardware, version and serial support
* QTECH: Fix platform and software version detection
* QTECH: Add test for QSW-3450