A mystery pooper has turned Broadway into the Great Wipe Way, laying waste to audition rooms by using them as a personal potty — and revolting thespians. The stealthy stink bomber struck during tryouts for the “Magic Mike” musical at Pearl Studios at 500 Eighth Ave. on Feb. 26, and again on March 6 at the Ripley-Grier space down the block. “There was a lot of disbelief,” said actress Eunice Bae of the first incident, when she saw a show rep slip on something on the floor. “She stopped and said, ‘Oh, I just stepped in s–t.’ We all laughed...