Looks like the connection to repository has not been successfully established.
Show details about the error by:
$ URLGRABBER_DEBUG=1 yum check-update
........
Temporary working around ... You could try with 1 of 2 options below:
1. Change the Extra Packages for Enterprise Linux (EPEL) configuration
locate epel.repo, example /etc/yum.repos.d/epel.repo
$vi /etc/yum.repos.d/epel.repo
Search for, and mask the mirrorlist:
#mirrorlist
Search for, and unmask the baseurl:
baseurl=....
2. Temporarily change the epel related files' names in /etc/yum.repos.d/
$ mv epel.repo epel.repo_bk
$ mv epel-testing.repo epel-testing.repo_bk
Then, go ahead to update.
$ yum clean all
$ yum update