Some improvements in the RPM packaging script.

- Install package epel-release to get the EPEL repo (rather than
  use a fixed URL).
- Use yum makecache fast to speed up caches for all repos.

pkg/rpm/pkg

@@ -40,13 +40,12 @@ cp /srv/vmod-selector.spec rpmbuild/SPECS
 cp /srv/vmod-selector-${VERSION}.tar.gz rpmbuild/SOURCES
 
 # install epel7 repo
-sudo yum install -y -q \
-     https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
+sudo yum install -y -q epel-release
 
 # set up varnish repo
 sudo cp /srv/varnishcache_varnish61.repo /etc/yum.repos.d/
 
-sudo yum -q makecache -y --disablerepo='*' --enablerepo='varnishcache_varnish61'
+sudo yum -q makecache -y fast
 
 # build requirements
 sudo yum install -y -q varnish-devel pkgconfig make gcc python-docutils