Nailgun documentation corrected
Nailgun documentation corrected

Section 8.1.1 "Setting up Environment" was corrected
so that to ensure that Nailgun tests pass and
Nailgun starts in fake mode.

The change set include detailed descriprion on how to
downgrade to Python 2.6, how to install missing packages,
and minor corrections such as cd, workon, apt-get update.

Change-Id: Ifea7436e516d5efdd2ff2ede5a50c1c0fb4db8a2
Closes-Bug: #1393582

prmtl/fuel-web,stackforge/fuel-web,nebril/fuel-web,SmartInfrastructures/fuel-web-dev,nebril/fuel-web,nebril/fuel-web,nebril/fuel-web,eayunstack/fuel-web,SmartInfrastructures/fuel-web-dev,prmtl/fuel-web,SmartInfrastructures/fuel-web-dev,eayunstack/fuel-web,prmtl/fuel-web,huntxu/fuel-web,zhaochao/fuel-web,SmartInfrastructures/fuel-web-dev,eayunstack/fuel-web,prmtl/fuel-web,huntxu/fuel-web,stackforge/fuel-web,prmtl/fuel-web,zhaochao/fuel-web,zhaochao/fuel-web,huntxu/fuel-web,stackforge/fuel-web,zhaochao/fuel-web,huntxu/fuel-web,SmartInfrastructures/fuel-web-dev,nebril/fuel-web,eayunstack/fuel-web,eayunstack/fuel-web,zhaochao/fuel-web,huntxu/fuel-web