put all configuration into a subdirectory
do not pass default config files

oslo.cfg does this work for use, therefore it is not needed to pass a
default config files list to the CONF object.
do not fail if we receive a datetime.datetime object

If somebody is not using an extract_from option, the upper manager will
try to read and parse the lastrun file, and we are going to get a
datetime.datetime object, that cannot be parsed by dateutil.parser. This
is a quick patch so that we do not fail, but this need to be refactored
though.
first set of unit tests
Merge pull request #2 from alvarolopez/master

Sync with development branch