Fix epel repo issue

[jlefevre]

Builds are failing frequently due to mirror issues.

Step 3/5 : RUN yum update -y &&     yum install -y https://apache.bintray.com/arrow/centos/7/apache-arrow-release-latest.rpm &&     yum install -y       re2-devel       arrow-devel       parquet-devel &&     yum clean all
 ---> Running in 5b90ef187d1a
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
 * base: mirror.netdepot.com
 * epel: mirror.team-cymru.com
 * extras: mirror.grid.uchicago.edu
 * updates: mirror.compevo.com
http://mirror.team-cymru.com/epel/7/x86_64/repodata/repomd.xml: [Errno -1] repomd.xml does not match metalink for epel
Trying other mirror.
https://linux-mirrors.fnal.gov/linux/fedora/epel/7/x86_64/repodata/repomd.xml: [Errno -1] repomd.xml does not match metalink for epel
Trying other mirror.

logfiles attached: travis.err.build54.log travis.err.build56.log

[jlefevre]

Closing this since transient repo issue is no longer happening.