make DHCP able to assign static IP to domains

Domain can now have IP addresses assigned statically for each network
they are connected to.
add create_network() function in cloubed library

This could be usefull for some use cases such as parallel boot_vm() on
domains that share the same network for instance.
add new cleanup() function in cloubed library

Exactly similar to cleanup action on cloubed script.
catch error on HTTPServer launch with warn message
add support of global testbed templates variables
templates vars and files should be both optionals
add support of templates domain contextual vars

This may help a lot for sharing templates between multiples domains.
release v0.2

Version bump in setup.py and RELEASE_NOTES file