Don't ignore environment variables pointing to valid configuration files. Fixes saltstack/salt-cloud#661

`salt.config.load_config()` cannot be hard-coded to use only the master configuration file as the default configuration file path to know if the user has passed any configuration file in the CLI tool or not.
To fix this, `default_path` was added. This way, the minion config or client config or even the salt cloud config can say which is the expected default path of the configuration file and properly load config from environment variables.
Merge pull request #5816 from mgwilliams/pillar-include-defaults

nesting for pillar includes
Fix more class refs to the Shell class
Tie off some minor additions here
Remove the evil dash of doom

Good catch, @s0undt3ch!  =)
Merge pull request #5818 from basepi/releasedocs

Remove the evil dash of doom
Fix traceback on non-yum systems

3b8b6de added yum.rpmtrans.RPMBaseCallback as a base class for
the _YumLogger class, which causes tracebacks on non-yum systems. This
commit fixes that by only creating this class if the yum python
interface is successfully imported.
Merge pull request #5819 from terminalmage/quickfix

Fix traceback on non-yum systems
Make openSUSE <12.1 use sysvinit for service mgmt

This fixes #5801 by checking the major release of the distro, if the
minion is openSUSE.
Merge pull request #5821 from terminalmage/issue5801

Make openSUSE <12.1 use sysvinit for service mgmt
Resolve Issue #5822
Merge pull request #5823 from quantumsummers/develop

Resolve Issue #5822
`ensure_in_syspath` now accepts multiple paths. Make use of it.
Merge pull request #5815 from s0undt3ch/develop

Don't ignore environment variables pointing to valid configuration files
Remove hyperlink until new link is found
Merge pull request #5826 from UtahDave/develop

Remove hyperlink until new link is found
Fix folder name for external pillars in docs
Update ext_pillar location in manpage
Merge pull request #5828 from elbaschid/fix/docs_for_external_pillar

Fix folder name for external pillars in docs
Documentation fix

This fixes #5827 by specifying the proper name for the software package
which provides add-apt-repository. It may have at one point been called
software-properties-common, but Ubuntu's package search page has
packages going back to 10.04 LTS showing add-apt-repository in the
python-software-properties package.