cmake is the dep for Fedora but cmake3 is for CentOS 7.
Centos: explicitly install epel-release on Centos.
Epel requirement is now explicit for cmake3, and ninja-build.
Remove references to Fedora 25 which is EOL.
Change-Id: I1548ddf2e5421097ac0ddc2d99abce7582d0d593 Signed-off-by: Thomas F Herbert <therbert@redhat.com>