Learn English – what does “First quality” mean

The usage of First Class in programming languages and frameworks is taken from First Class Citizen, and is used to refer to concepts or mechanisms that are baked into the design of the language or framework.

I'll try to illustrate this with a programming-focused example, since your question referred to a programming framework (Hadoop). In the C language, you don't have text as first-class citizens, but only arrays of characters that are treated as strings. Newer programmming languages, like Java or C#, have strings as first-class citizens, built into the language rather than bolted on later.

A slightly less technical example might be tags/hashtags. Here on StackExchange, tags are first class citizens - each question has tags that can be used to search, filter, award badges, etc. On Twitter, however, hashtags started as just the text "#whatever" in a tweet, without any actual technical meaning - only later did Twitter adopt them as official features. They're not first-class citizens of the platform.

So in your original context, I would say that Hadoop treats software and hardware failures, not as external situations that disrupt the regular order of operation, but as part of the process, something that is integrated into the platform and can be handled normally.

I don't think it is possible to know exactly what the commentator meant without asking him or her, but there are several possibilities. An uber-word could be:

1. a superlative word (which was how I initially understood it)
2. a trendy word (that pushes out the native one for a while)
3. a "cuckoo" word that usurps all native words

It's this last one that I'm leaning towards at the moment, as this is how the taxi firm operates, and this is the most well known use of the word uber at the moment.