fix: use absolute paths for coverage and test-results directories

The test-junit and test-coverage recipes were failing because they used
relative paths (../coverage/) which don't work correctly when cd'ing into
subdirectories. When in cmd/morphir, ../coverage/ points to morphir/cmd/coverage/
instead of morphir/coverage/.

Now we capture the repo root path upfront and use absolute paths for all
coverage and test result file locations.

Author: DamianReeves