Replace /build/source by /build/ironos to eliminate ambiguity with /build/source/source

[ia]

• Please check if the PR fulfills these requirements

• The changes have been tested locally
• There are no breaking changes

• What kind of change does this PR introduce?
  Tiny change of the directory name inside docker container.

• What is the current behavior?
  The root project directory mapped/copied to /build/source/ inside of docker container. But since there is source directory inside the root project directory already, sometimes it leads to ambiguity.

• What is the new behavior (if this is a feature change)?
  The root project directory mapped/copied to /build/ironos inside of docker container.
  Plus tiny refactoring buildAll.sh only to use variables for directories instead of hardcoded paths just in case.

• Other information:
  Just another one tiny "ci beautify" suggestion. :)
  It shouldn't affect anything else though - I tested it locally by running make docker-build and all output files have been generated where they supposed to be.