Set default CentOS7 Vault build to 7.6

Author: oneswig

elements/centos7-vault/README.rst

@@ -9,21 +9,21 @@ the baseline for built disk images.
 
 DIB_CENTOS7_VERSION:
   :Required: No
-  :Default: 7.7
+  :Default: 7.6
   :Description: Set a version, from 7.1 to 7.7 (inclusive) and the last-known
                 public locations for package repos and cloud images will be used.
 
 DIB_CENTOS7_MIRROR_VERSION:
   :Required: No
-  :Default: 7.7.1908
+  :Default: 7.6.1810
   :Description: Set a fully-qualified version for a build of CentOS.
                 A sensible last-known default value is set according to 
                 ``DIB_CENTOS7_VERSION``.  This value also overwrites
                 ``$releasever`` in a standard ``CentOS-Base`` yum repo.
 
 DIB_CENTOS7_CLOUDIMAGE_VERSION:
   :Required: No
-  :Default: GenericCloud-1907
+  :Default: GenericCloud-1811
   :Description: Set a fully-qualified version for a cloud image build.
                 A sensible last-known default value is set according to 
                 ``DIB_CENTOS7_VERSION``.

elements/centos7-vault/environment.d/10-centos7-distro-name.bash

@@ -4,7 +4,8 @@ export DIB_RELEASE=7
 # Useful for elements that work with fedora (dnf) & centos
 export YUM=${YUM:-yum}
 
-export DIB_CENTOS7_VERSION=${DIB_CENTOS7_VERSION:-"7.7"}
+# At the time of writing CentOS 7.7 is still current and the vault content is incomplete.
+export DIB_CENTOS7_VERSION=${DIB_CENTOS7_VERSION:-"7.6"}
 case "$DIB_CENTOS7_VERSION" in
     7.7)
         DIB_CENTOS7_MIRROR_VERSION=${DIB_CENTOS7_MIRROR_VERSION:-"7.7.1908"}