display informative error message if schedule fails to deep_merge

Display the two yaml structures that fail to merge in case of an
exception. That's a useful hint to find out what's wrong.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
Merge pull request #344 from dachary/wip-9842-deep-merge

display informative error message if schedule fails to deep_merge
Require six >= 1.5.0

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add separate install documentation

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Rewrite description and overview

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add "Provided utilities" section

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add "Choosing machines for a job" section

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Remove old install instructions

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>