Don't fail integration tests if the subject is not passing its own tests

As suggested in https://github.com/rust-lang-nursery/rustfmt/pull/2715#issuecomment-390397152

ci/integration.sh

@@ -21,6 +21,10 @@ echo "Integration tests for: ${INTEGRATION}"
 cargo fmt -- --version
 
 function check_fmt {
+    cargo test --all
+    if [[ $? != 0 ]]; then
+          return 0
+    fi
     touch rustfmt.toml
     cargo fmt --all -v 2>&1 | tee rustfmt_output
     if [[ $? != 0 ]]; then