Robustify shocco install and config

* shocco has some non-optional prereqs, make sure they are present if
shocco is being installed
* set the path to installed shocco correctly
* add the working dir to .gitignore

Change-Id: If786ea9e28d3595775f7b86d2fe760dff8047f49
Merge "Robustify shocco install and config"