Sync only missing blocks on cold import

= Add eth_node_fingerprint to block that can be imitated by both hot and cold imports
- Only sync missing blocks (blocks that are missing or don't share a fingerprint) on cold import
- Set block is_final status after import

pkg/fakes/mock_fs_reader.go

@@ -0,0 +1,38 @@
+package fakes
+
+import . "github.com/onsi/gomega"
+
+type MockFsReader struct {
+	readCalled      bool
+	readPassedPath  string
+	readReturnBytes []byte
+	readReturnErr   error
+}
+
+func NewMockFsReader() *MockFsReader {
+	return &MockFsReader{
+		readCalled:      false,
+		readPassedPath:  "",
+		readReturnBytes: nil,
+		readReturnErr:   nil,
+	}
+}
+
+func (mfr *MockFsReader) SetReturnBytes(returnBytes []byte) {
+	mfr.readReturnBytes = returnBytes
+}
+
+func (mfr *MockFsReader) SetReturnErr(err error) {
+	mfr.readReturnErr = err
+}
+
+func (mfr *MockFsReader) Read(path string) ([]byte, error) {
+	mfr.readCalled = true
+	mfr.readPassedPath = path
+	return mfr.readReturnBytes, mfr.readReturnErr
+}
+
+func (mfr *MockFsReader) AssertReadCalledWith(path string) {
+	Expect(mfr.readCalled).To(BeTrue())
+	Expect(mfr.readPassedPath).To(Equal(path))
+}