INVESTMENT AGREEMENT by and among 21VIANET GROUP, INC. and VECTOR HOLDCO PTE. LTD. and BTO VECTOR FUND ESC (CYM) L.P. and BTO VECTOR FUND FD (CYM) L.P. and BLACKSTONE TACTICAL OPPORTUNITIES FUND — FD (CAYMAN) — NQ L.P. Dated as of June 22, 2020