move all package installation to postinst

var/local/mkosi/mkosi.default

@@ -16,20 +16,4 @@ UseHostRepositories=True
 
 [Content]
 WithNetwork=True # needed to run yum install in postinst
-Packages=
-    yum
-    curl
-    gperftools
-    hostname
-    xrootd-server-5.1.0
-    xrootd-client-5.1.0
-    xrootd-5.1.0
-    xrootd-voms-5.1.0
-    xrootd-libs-5.1.0
-    voms-clients
-    wlcg-voms-atlas
-    fetch-crl
-    #osg-ca-certs # not sure where this comes from and if it's needed
-    gdb
-    yum-utils
-    python-requests
+Packages=yum

var/local/mkosi/mkosi.postinst

 #!/bin/bash
 
-yum --releasever=7 --enablerepo="osg-upcoming-testing" install -y xrootd-rucioN2N-for-Xcache-1.2-3.3.osg35up.el7.x86_64
+yum install -y --releasever=7 \
+    curl \
+    gperftools \
+    hostname \
+    xrootd-server-5.1.0 \
+    xrootd-client-5.1.0 \
+    xrootd-5.1.0 \
+    xrootd-voms-5.1.0 \
+    xrootd-libs-5.1.0 \
+    voms-clients \
+    wlcg-voms-atlas \
+    fetch-crl \
+    gdb \
+    yum-utils \
+    python-requests
+
+yum --releasever=7 --disablerepo="*" --enablerepo="osg-upcoming-testing" install -y xrootd-rucioN2N-for-Xcache-1.2-3.3.osg35up.el7.x86_64