(PUP-2218) Use /etc/yum.conf for yumrepo default location
(maint) refactor find_conf_value to use PhysicalFile
(maint) Update yumrepo inifile provider comments
(maint) expand yumrepo inifile inline documentation.
Merge branch 'bugfix/stable/pup-2218-yumrepo-use-yumconf' into stable