Unified repo keyservers.
Instead of having some third-party keyserver for docker repository,
changed the key server to be the same as for the rest of the
repositories. Ubuntu keyserver contains the same key.

Change-Id: I3639f96ce50c63e57d9fb84badb879d845b2d787
diff --git a/linux/system/repo/docker.yml b/linux/system/repo/docker.yml
index 6eae575..c527aa8 100644
--- a/linux/system/repo/docker.yml
+++ b/linux/system/repo/docker.yml
@@ -6,4 +6,4 @@
           source: "deb https://apt.dockerproject.org/repo ubuntu-${_param:linux_system_codename} main"
           architectures: amd64
           key_id: 58118E89F3A912897C070ADBF76221572C52609D
-          key_server: hkp://p80.pool.sks-keyservers.net:80
+          key_server: keyserver.ubuntu.com