Merge pull request #1586 from dongluochen/update_swarm_v1.2.0-rc2

update swarm v1.2.0-rc2

library/swarm

@@ -11,4 +11,5 @@
 1.1.2: git://github.com/docker/swarm-library-image@5f284e33ef90b7bc30684ad09a5261c037fc9d5e
 1.1.3: git://github.com/docker/swarm-library-image@4d298d3113a4ecefa83a3f9e18f4aaf4f95f007e
 1.2.0-rc1: git://github.com/docker/swarm-library-image@703192c7907b3d30e20d68a8353b25110a2a290c
+1.2.0-rc2: git://github.com/docker/swarm-library-image@1b528de8de78dc6a3e8159c204c12b84dad43710
 latest: git://github.com/docker/swarm-library-image@4d298d3113a4ecefa83a3f9e18f4aaf4f95f007e