Nitrogen chain nomenclature
According to the IUPAC Gold book, these are known as azanes, from the information:


  Saturated acyclic nitrogen hydrides having the general formula $\ce{N_{n}H_{n + 2}}$


For the example you are looking at, according to the IUPAC document P-67 Mononuclear and polynuclear noncarbon acids and their functional replacement
analogues as parents for naming organic compounds (p. 15) is named as 2-aminotriazane.