Add OWNERS to libraries that did not have it.

Test: None
Change-Id: I48b73aa12ee86576a440290a92fbda70347c811a
diff --git a/concurrent/OWNERS b/concurrent/OWNERS
new file mode 100644
index 0000000..36f79b6
--- /dev/null
+++ b/concurrent/OWNERS
@@ -0,0 +1 @@
[email protected]
\ No newline at end of file