Renaming HOME env variable due to the collision with root env variable

Fixing the HOME varialbe collision by renaming the variable into STI_HOME as suggested by Andy.
This is one of the possible solutions. Another one is to hardcode the path into the assemble script which PR also sent. 
If we decide that this is the right solution for this issue I will close the second PR and vice versa.

I tested this solution and its working - the artifacts are properly saved and restored.