Separate extras yum repo from other official repos
Separate extras yum repo from other official repos

Sometimes it is necessary to enable extras yum repository while it is
disabled by default. The most convenient way is to set YUM_REPOS
variable for a particular job. This patch makes it possible.

Change-Id: Icb074474fa4602288aa43129dd1dfc058ebe646b

eayunstack/fuel-main,stackforge/fuel-main,huntxu/fuel-main,stackforge/fuel-main,SergK/fuel-main,huntxu/fuel-main,SergK/fuel-main,eayunstack/fuel-main,huntxu/fuel-main,SergK/fuel-main,eayunstack/fuel-main,stackforge/fuel-main