Refactor test structure per some review feedback.

Author: thedodd

rustfmt-core/rustfmt-lib/tests/source/configs/space_around_attr_eq/false.rs

@@ -0,0 +1,6 @@
+// rustfmt-space_around_attr_eq: false
+
+fn attr_eq_test() {
+    #[cfg(not(target_os = "pi"))]
+    println!("os is not pi!");
+}

rustfmt-core/rustfmt-lib/tests/source/space_around_attr_eq.rs renamed to rustfmt-core/rustfmt-lib/tests/source/configs/space_around_attr_eq/true.rs

@@ -0,0 +1,6 @@
+// rustfmt-space_around_attr_eq: false
+
+fn attr_eq_test() {
+    #[cfg(not(target_os="pi"))]
+    println!("os is not pi!");
+}