Added documentation about installing a CentOS VM and a CTA Environment

continuousintegration/buildtree_runner/vmBootstrap/InstallCTAEnvironment.md

+## Install a CentOS VM on CentOS
+
+*Source: https://www.linuxtechi.com/install-kvm-hypervisor-on-centos-7-and-rhel-7/*
+
+1. Download the CERN Centos here : http://linuxsoft.cern.ch/cern/centos/7/os/x86_64/images/boot.iso
+
+2. Install Virtual Machine Manager and KVM / QEMU related libs :
+```bash
+sudo yum install qemu-kvm qemu-img virt-manager libvirt libvirt-python libvirt-client virt-install virt-viewer bridge-utils
+```
+
+3. Start and enable the libvirtd service :
+```bash
+sudo systemctl start libvirtd
+sudo systemctl enable libvirtd
+```
+
+4. Launch virt-manager by typing :
+```bash
+virt-manager
+```  
+5. Create a new virtual machine by clicking on the corresponding button
+- Choose Local install media
+- Use ISO image, browse
+- Set the Memory (RAM) you want (I suggest using 8192 Mib)
+- Set the number of CPU you want (I suggest 2)
+- Create a disk image for the virtual machine (choose the size you allocate for the disk)
+- Name the machine and click Finish
+
+6. Install the CERN CentOS following the instructions here : http://linux.web.cern.ch/linux/centos7/docs/install.shtml
+
+## Setting up CTA environment in your VM
+1. Clone the project from the CTA's gitlab page : https://gitlab.cern.ch/cta/CTA
+2. go to the CTA folder and init the xrootd-ssi-profobuf-interface submodule :
+```bash
+git submodule init
+git submodule update
+```
+
+3. Go to CTA/continuousintegration/buildtree_runner/vmBootstrap and type the following commands :
+```bash
+cp gitScripts/.git-* ~
+cat gitScripts/bash_profile.hook >> ~/.bash_profile
+source ~/.bash_profile
+cp tigConf/tigrc ~/.tigrc
+yum install -y git cmake rpm-build gcc gcc-c++ vim gdb cgdb strace ltrace screen tig lsscsi mt-st mtx sg3_utils jq psmisc yum-plugin-versionlock
+```
+4. Bootstrap CTA :
+```bash
+cat > ~/path_to_CTA_folder/.git/hooks/post-checkout << EOFGitHook
+#!/bin/sh
+cd `git rev-parse --show-toplevel`
+git submodule update --init --recursive
+EOFGitHook
+
+chmod +x ~/path_to_CTA_folder/.git/hooks/post-checkout
+
+cp ~/path_to_CTA_folder/.git/hooks/post-checkout ~/path_to_CTA_folder/.git/hooks/post-merge
+```
+5. Build CTA's srpm
+Go to the CTA parent's folder and type 
+```bash
+mkdir CTA-build-srpm
+cd CTA-build-srpm
+cmake -DPackageOnly:Bool=true ../CTA
+make cta_srpm
+```
+
+6. Install repositories necessary for CTA's compilation works
+```bash
+cd ~/path_to_CTA_folder/continuousintegration/buildtree_runner/vmBootstrap
+sudo yum-config-manager --add-repo=../../docker/ctafrontend/cc7/etc/yum.repos.d/eos-citrine-depend.repo 
+sudo yum-config-manager --add-repo=../../docker/ctafrontend/cc7/etc/yum.repos.d/cta-ci.repo
+sudo yum-config-manager --add-repo=../../docker/ctafrontend/cc7/etc/yum.repos.d/castor.repo
+sudo yum-config-manager --add-repo=ceph-internal.repo
+```
+7. Install yum-plugin-priorities
+```bash
+sudo yum install -y yum-plugin-priorities
+```
+
+8. Add versionlock for xrootd
+```bash
+sudo cp ../../docker/ctafrontend/cc7/etc/yum/pluginconf.d/versionlock.list  /etc/yum/pluginconf.d/versionlock.list
+```
+
+9. Install build dependencies
+10.Verify you have the CentOS-CERN.repo, epel.repo and elrepo.repo in /etc/yum.repos.d/
+Then, go to the CTA-build-srpm directory and execute :
+```bash
+sudo yum-builddep -y ./RPM/SRPMS/cta-0-1.src.rpm --nogpgcheck
+``` 
+10. Install mhvtl
+```bash
+sudo yum install -y mhvtl-utils kmod-mhvtl mhvtl-utils --enablerepo=castor
+```
+11. Build CTA
+Create a directory near the CTA one called CTA-build, go into it and type
+```bash
+cmake ../CTA
+make -j 4
+```
+12. Run the unit tests of CTA located in CTA-build/tests
+```bash
+./cta-unitTests
+```
+
+If tests don't run, edit the /etc/resolv.conf file and add a line with
+```
+search cern.ch
+```