init: do not log directly from read_file() and write_file()

Their callers may be able to add more context, so use an error string
to record the error.

Bug: 38038887
Test: boot bullhead
Test: Init unit tests
Change-Id: I46690d1c66e00a4b15cadc6fd0d6b50e990388c3
diff --git a/init/init_test.cpp b/init/init_test.cpp
index 3da14b5..7093ba9 100644
--- a/init/init_test.cpp
+++ b/init/init_test.cpp
@@ -152,10 +152,11 @@
                                "on boot\n"
                                "execute 3";
     // clang-format on
-    // write_file() ensures the right mode is set
-    ASSERT_TRUE(write_file(std::string(dir.path) + "/a.rc", dir_a_script));
+    // WriteFile() ensures the right mode is set
+    std::string err;
+    ASSERT_TRUE(WriteFile(std::string(dir.path) + "/a.rc", dir_a_script, &err));
 
-    ASSERT_TRUE(write_file(std::string(dir.path) + "/b.rc", "on boot\nexecute 5"));
+    ASSERT_TRUE(WriteFile(std::string(dir.path) + "/b.rc", "on boot\nexecute 5", &err));
 
     // clang-format off
     std::string start_script = "import " + std::string(first_import.path) + "\n"