Show binary name in "Unable to locate app binary" error message

[talpr]

Hi,

I was trying to run a reproduction for a Chrome ASAN failure, when I got the above error message. Having just built the Chrome binary, I was confused for a bit, until I took a closer look at the detailed testcase and noticed that it was actually running a different binary (content_shell, which is a simplified version of Chrome). Although I was able to figure it out myself, it would have been nice if the error message specified the binary it was trying to run and not just the directory it was looking in.