Fix install for CentOS 7.0.1406

    * Add extra case to the rpm_install to catch the latest centos
      - fixes install errors due to package key
      - points centos to specific location for epel-release
      - points other RHEL to own location for epel-release
Fix install for CentOS 7.0.1406

Conflicts:
	scripts/install-sysdig.in