Enforce all fingerprints to require examples

[dabdine]

Is your feature request related to a problem? Please describe.
Fingerprint elements in fingerprint XML files should always contain examples. Work has been done in previous PRs to settle many broken <example> tags. However, several other <fingerprint> XML elements are missing <example> elements altogether. We should enforce that examples are always present.

Describe the solution you'd like

1. Update all fingerprint files to have an example, even if the data must be mocked (with an XML comment indicating as such).
2. Update fingerprints.xsd after Enable fingerprint xsd validation and CI automation #410 is merged so that minOccurs on <example> is 1 instead of 0: https://github.com/rapid7/recog/blob/master/xml/fingerprints.xsd#L106. With this simple change, once Enable fingerprint xsd validation and CI automation #410 lands the XML schema validation logic in recog_verify should automatically flag any missing example elements as an error (thus, giving developers immediate feedback & ensuring CI PR builds fail if one is not included).

Describe alternatives you've considered
None.

Additional context
Clearing out all warnings & errors from the existing XML fingerprint files should help greatly in enforcing strict standards for new fingerprints that are added, and ultimately ensure recog is kept high quality.