When cargo errors, print an error about cargo.out.

Currently if cargo produces an error it's not obvious how to debug it.
Add a message telling the user to look at the cargo.out file, which
has its output.

Test: Ran on crates with and without errors
Change-Id: Ib681a8e87f60467c7425aed5f7e5277a0603bcc8
1 file changed