BaseImageManager's init function used to take two arguments:
'config_files' and 'images' in that order. Commit
08a8118f1b added another one in between
the two, 'template_dir'.
ImageBuildManager inherits from BaseImageManager and calls its init
function with 'config_files' and 'images' as positional arguments, which
no longer works because 'images' is now the third argument. Therefore
the value passed as 'images' gets quietly written as 'template_dir'
instead.
Passing 'images' as a keyword argument instead solves the issue.
Change-Id: I591345985ccbb8ebfdf9848104478ec1aadb4a7f
6939ec8b46