Use Fabric's cd on setup_default_capsule task

Improve the setup_default_capsule task to use the cd context manager to
change directory.

This important comment https://github.com/SatelliteQE/automation-tools/pull/64#discussion_r20863634 was missed on last PR. Thanks @omaciel for the sharp eyes.
that is interesting. does it run the following commands after performing the cd, then return to the previous directory ?