Don't try to use/write to /var/cache/yum.

Use a local directory instead.

libguestfs.spec

@@ -891,7 +891,7 @@ ip route list ||:
 if ping -c 3 -w 20 8.8.8.8 && wget http://libguestfs.org -O /dev/null; then
   extra=
 else
-  mkdir repo
+  mkdir cachedir repo
   # -n 1 because of RHBZ#980502.
   find /var/cache/{dnf,yum} -type f -name '*.rpm' -print0 | \
     xargs -0 -n 1 cp -t repo

yum.conf.in

@@ -1,7 +1,7 @@
 [main]
-cachedir=/var/cache/yum
+cachedir=@PWD@/cachedir
 debuglevel=1
-logfile=/var/log/yum.log
+logfile=@PWD@/yum.log
 retries=20
 obsoletes=1
 gpgcheck=0