Fixes an import bug with the DNS_ETW auxiliary module (#2293)

* Fixes an import bug with the DNS_ETW auxiliary module
DNS_ETW references several entities that are part of the pywintrace library. If the pywintrace library isn't present on the VM, the analyzer fails when attempting to import the DNS_ETW module.

This change moves the code that references pywintrace into a conditional statement, to prevent the analyzer from exiting prematurely.

* Rename DNS_ETW to dns_etw

Author: josh-feather