By Luc Cohen and Joel Schectman NEW YORK/WASHINGTON (Reuters) -An Iranian-American journalist and women’s rights activist said it was “shocking” to learn that a man had been arrested last week with a loaded AK-47 rifle outside her Brooklyn, New York, home. The journalist, Masih Alinejad, last year was said to be the target of a Tehran-backed kidnapping plot. Alinejad has promoted videos of women violating Iran’s head covering law to her millions of social media followers. Khalid Mehdiyev spent two days last week outside the home, and at one point attempted to open the door, an FBI agent wrote …