[build_init] Support .textproto suffix

Bug: IN-1227 #comment
Change-Id: Ib03c852f97a3fecc09bdb877351d3919710c35ab
diff --git a/cmd/build_init/main.go b/cmd/build_init/main.go
index e5b9899..0593a77 100644
--- a/cmd/build_init/main.go
+++ b/cmd/build_init/main.go
@@ -130,8 +130,14 @@
 	}
 	specPath := filepath.Join(specDir, build.Builder.Bucket, build.Builder.Builder)
 	if _, err := os.Stat(specPath); os.IsNotExist(err) {
-		log.Printf("file not found %v", specPath)
-		return ExitFileNotFound
+		// TODO(IN-1227): Make this the only supported suffix.
+		// TODO(IN-1227): Add a .textproto file to the test project and roll the commits in integration tests.
+		withSuffix := specPath + ".textproto"
+		log.Printf("file not found %v. Trying %v", specPath, withSuffix)
+		if _, err := os.Stat(withSuffix); os.IsNotExist(err) {
+			log.Printf("file not found %v", withSuffix)
+			return ExitFileNotFound
+		}
 	}
 	fd, err := os.Open(specPath)
 	if err != nil {