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/property_service.cpp b/init/property_service.cpp
index 6f40d1c..e01cd0b 100644
--- a/init/property_service.cpp
+++ b/init/property_service.cpp
@@ -510,8 +510,9 @@
 static void load_properties_from_file(const char* filename, const char* filter) {
     Timer t;
     std::string data;
-    if (!read_file(filename, &data)) {
-        PLOG(WARNING) << "Couldn't load properties from " << filename;
+    std::string err;
+    if (!ReadFile(filename, &data, &err)) {
+        PLOG(WARNING) << "Couldn't load property file: " << err;
         return;
     }
     data.push_back('\n');