NEW YORK — Embattled actor Kevin Spacey took the witness stand Monday at his Manhattan trial, where he launched into his testimony by revealing his rocky relationship with a “neo-Nazi” father who verbally abused him because he suspected his son was gay. Spacey, who is being sued in Manhattan federal court by actor Anthony Rapp in a $40 million civil lawsuit that claims the older actor aggressively came on to him in 1986 when he was 14, told jurors that his father was a white supremacist who ”used to yell at me about the idea I might be gay because I was interested in theater, and he didn’t enc…