conf dict not Configuration attribute anymore

The conf loaded by ConfigurationLoader does not need to an attribute of
Configuration objects anymore.
new method to parse storage pool path in YAML

Added new method ConfigurationPool.__parse_path() to better parse
storage pools paths in YAML.
make sure everything is a string in templates dict
fix wrong exception name

NotImplemented is not an exception, NotImplementedError is.
clean-up + default spice in __parse_graphics()

Some clean-up in Configuration.__parse_graphics() and also set default
value to 'spice' if not defined in YAML.
new method to parse domains templates in YAML

Added new method ConfigurationDomain.__parse_templates() to better
parse domains template files and variables in YAML.
new methods to parse storage volumes in YAML

Added several new methods ConfigurationStorageVolume.__parse_*() to
better parse storage volumes attributes in YAML.
fix string equality tests
various clean-ups in domains parsing methods

Some clean-ups and homogenisation over ConfigurationDomain.__parse_*()
methods.

Also handles more errors (like missing attributes).

Finally, this commit adds missing docstrings.
avoid tracking of coverage file in git
first set of unit tests

These first unit tests cover 100% of lib/conf sub-module for the
parsing of YAML files.
print additional information with cloubed status

status action of cloubed script now prints complementary information
about the resources of the testbed, additionally to their status in
Libvirt.

Fixes #10.
add new Utils module with utility functions

Moved gen_mac() into it.
add new utility getuser() and use it everywhere

This replaces sometimes buggy os.getlogin().

Fixes #20.