python34_update: Updated build scripts for Centos and RHEL to python34

python34_update: Updated build scripts for Centos and RHEL to python34

Recent patch update to collectd requires new packages that must
have python34 as a minimum version available. This updates the
build scripts for Centos and RHEL to use scl enabled python34.

1. Adds needed packages to build correctly for Centos and RHEL
2. Changes repo location to pull scl enabled python34
3. Modifies enablement of scl to new package string
4. Updates documentation to reflect change

JIRA: VSPERF-558

Change-Id: I52257ecfc6abc2112c30137c1de3ced272f21066
Signed-off-by: Christian Trautman <ctrautma@redhat.com>