What is the term used to define an answer which does not offend anyone?

I would call it diplomatic

Diplomatic: Of or concerning diplomacy:

Diplomacy: The art of dealing with people in a sensitive and tactful way

(Definitions from http://www.oxforddictionaries.com/ and not the only definitions of those words)

A neutral answer is generally given not to take sides with any of the party involved:

• belonging to neither side in a controversy: on neutral ground.
• belonging to neither kind; not one thing or the other.

The Free Dictionary

or a diplomatic answer may refer an answer which tries to avoid possible conflicts:

• Using or marked by tact and sensitivity in dealing with others. (AHD)

A answer that is politically correct usually implies it won't offend most people. It does not imply anything abut politics.