Added CentOS specific build requirements

[WhiteyDude]

devtoolset-6 for make, specific packages, cmake3 with alternatives set

Fixes drachtio/drachtio-server#86 and drachtio/drachtio-server#71

[davehorton]

I'm trying to test these changes on a Red Hat Enterprise Linux release 8.0 (Ootpa) VM and getting this error:

TASK [ansible-role-drachtio : CentOS family - Install GC 6.x] ***************************************************************************************************************
fatal: [52.54.225.136]: FAILED! => {"changed": false, "failures": ["No package devtoolset-6-gcc-c++ available."], "msg": "Failed to install some of the specified packages", "rc": 1, "results": []}

Are there some version dependencies that we need to be aware of? i.e. do we only need to install these gcc/g++ versions for some of the older centos/rh distros ?

[ivlovric]

This works for me on Centos 7 and hope it will be helpful for others.
main.yml.zip