Merge tag 'sparks-2.7.7' into develop

2.7.7
Add a wrapped ``sed`` task, to be executed in the virtualenv (not that useful) and ch'ed into the environment's root (THAT is more useful), and on all the machines of sparks roles (YEAH! That's *really* useful).
bump version number for development branch.
More comments and docstrings updates.
new lxc_purge() task.
bump version in __init__.py
Merge branch 'release/2.8'