Improve ImageManager error message

Print more helpful error messages to logcat.

Bug: 165471299
Test: Observe logcat
Change-Id: I3dca834a7cd3f653b038fc3a4020e96f500e1d1f
diff --git a/fs_mgr/libfiemap/image_manager.cpp b/fs_mgr/libfiemap/image_manager.cpp
index f32e0eb..93fc131 100644
--- a/fs_mgr/libfiemap/image_manager.cpp
+++ b/fs_mgr/libfiemap/image_manager.cpp
@@ -640,16 +640,22 @@
         return false;
     }
 
+    bool ok = true;
     for (const auto& partition : metadata->partitions) {
         auto name = GetPartitionName(partition);
         auto image_path = GetImageHeaderPath(name);
         auto fiemap = SplitFiemap::Open(image_path);
-        if (!fiemap || !fiemap->HasPinnedExtents()) {
-            LOG(ERROR) << "Image is missing or was moved: " << image_path;
-            return false;
+        if (fiemap == nullptr) {
+            LOG(ERROR) << "SplitFiemap::Open(\"" << image_path << "\") failed";
+            ok = false;
+            continue;
+        }
+        if (!fiemap->HasPinnedExtents()) {
+            LOG(ERROR) << "Image doesn't have pinned extents: " << image_path;
+            ok = false;
         }
     }
-    return true;
+    return ok;
 }
 
 bool ImageManager::DisableImage(const std::string& name) {