Set right priorities to ubuntu repos.

Priority of repos created by fuel-mirror are incorrect.
That fix syncs priorities with fuel-web code from commit
I1666803b91d86247ac13066fc42ae12fa7377dbb

Change-Id: I45a6b7915d629d966784c63b49eae6b3efd0d849
Partial-Bug: #1661399

contrib/fuel_mirror/data/ubuntu.yaml

@@ -41,7 +41,7 @@ repos:
         suite: "mos$mos_version"
         section: "main restricted"
         type: "deb"
-        priority: 1000
+        priority: 1050
 
     -   &mos_updates
         name: "mos-updates"
@@ -49,7 +49,7 @@ repos:
         suite: "mos$mos_version-updates"
         section: "main restricted"
         type: "deb"
-        priority: 1000
+        priority: 1050
 
     -   &mos_security
         name: "mos-security"
@@ -57,7 +57,7 @@ repos:
         suite: "mos$mos_version-security"
         section: "main restricted"
         type: "deb"
-        priority: 1000
+        priority: 1050
 
     -   &mos_holdback
         name: "mos-holdback"
@@ -65,7 +65,7 @@ repos:
         suite: "mos$mos_version-holdback"
         section: "main restricted"
         type: "deb"
-        priority: 1000
+        priority: 1100
 
 # Packages are required to build bootstrap images for a system.
 # The mirror should contiain such packages in addition to local mirror.