Little update on the build platform

[Erwan Velu <evelu@redhat.com>]

Hi folks,

Just a short email to mention several updates that have been pushed to the build platfrorm 
- build VMs are now generated by the edeploy (https://github.com/redhat-cip/edeploy) project
- centos 7, ubuntu {trusty|xenial} are now built with the same automated procedure
- xfs is becoming the default rootfs of those VMs
- build requires are already installed reducing the time required by install-deps.sh
- An diagnosis helper is now in place to spot known build failures  :
A list of common issues have been entered (like gcc or jenkins failures, segfaults, etc...)
A typical output looks like : https://jenkins.ceph.com/job/ceph-pull-requests/6448/
If you find new build failures, feel free to ping me to add them.
This helps at finding build issues in a second while the build logs are pretty long to read.

All that improvements are targeting a more reliable build system.

Please note that we have a lot of segfaults during the builds, if some can have a look around that would be lovely.

Erwan,