[oni-scheme] Print output of integration tests for debugging

In bats, when you print to stdout during a test, if the test fails bats will
show the output that was generated. If everything succeeds it hides the output.

test/integration/oni-scheme.bats

@@ -5,6 +5,8 @@
           -visit test.scm \
           -eval "(prin1 (featurep 'oni-scheme))"
 
+    echo "$output"
+
     [ "$output" = "t" ]
 }
 
@@ -19,5 +21,7 @@
 
     rm "$filename"
 
+    echo "$output"
+
     [ "$output" = "scheme-mode" ]
 }