enum_ad_* post module fixes

[Meatballs1]

#3175 broke enum_ad_* post modules as it changed the return type from the ADSI queries.

Fixes: #4387

Poke @OJ @bcook-r7

This also modifies the legacy Railgun LDAP implementation so it returns data in the same format.

Verification

• Run enum_ad_computers - results should be hashes :(
• Apply PR
• enum_ad_computers, enum_ad_user_comments, enum_ad_service_principal_names and enum_ad_to_wordlist - results should be as expected

[jhart-r7]

It may be worth starting to add some unit tests to spec/lib/msf/core/post/windows/ldap.rb

[Meatballs1]

Would be painful as all the data is pretty much from an active session. If someone wants to mock railgun/extapi...

[bcook-r7]

Thanks a lot, taking a look now. Mocking extapi sounds like 'ecstasy' according to my spell checker.