Add additional empty line between pinning rules for extra repos

Additional empty line is needed for pinning rules to be correctly used

Change-Id: I8360b904ac4de6f55c164de3a0b84bd3291da848
diff --git a/src/com/mirantis/mk/Common.groovy b/src/com/mirantis/mk/Common.groovy
index 09f1b51..25ab212 100644
--- a/src/com/mirantis/mk/Common.groovy
+++ b/src/com/mirantis/mk/Common.groovy
@@ -962,6 +962,8 @@
                     repoPins.add("Package: ${pin['package']}")
                     repoPins.add("Pin: ${pin['pin']}")
                     repoPins.add("Pin-Priority: ${pin['priority']}")
+                    // additional empty line between pins
+                    repoPins.add('\n')
                 }
                 if (repoPins) {
                     repoPins.add(0, "### Extra ${repo} repo pin start ###")