Update Makefile to use pytest for unit testing

Replace nosetests with pytest and simplify the cleanup logic for temporary test directories.

Author: calvinp0

Makefile

@@ -1,6 +1,3 @@
 unittest unittests test-unittest test-unittests:
-	nosetests --nocapture --nologcapture --all-modules --verbose --with-coverage  --cover-package=autotst 
-	rm -r species
-	rm -r ts
-	rm -r test/species
-	rm -r test/ts
+	pytest --verbose --tb=short autotst/
+	rm -rf species ts test/species test/ts