device tests: updates for esptool.py (#6084)

Makefile new rule: 'make distclean' removes virtualenv
attempt to use python3 (python2 is still default)

tests/device/libraries/BSTest/Makefile

@@ -1,5 +1,6 @@
 PYTHON_ENV_DIR=virtualenv
 TEST_EXECUTABLE=test/test
+PYTHON ?= python3
 
 all: test
 
@@ -10,7 +11,7 @@ clean:
 	rm -rf $(TEST_EXECUTABLE)
 
 $(PYTHON_ENV_DIR):
-	virtualenv --no-site-packages $(PYTHON_ENV_DIR)
+	virtualenv --python=$(PYTHON) --no-site-packages $(PYTHON_ENV_DIR)
 	. $(PYTHON_ENV_DIR)/bin/activate && pip install -r requirements.txt
 
 test: $(TEST_EXECUTABLE) $(PYTHON_ENV_DIR)

tests/device/libraries/BSTest/runner.py

@@ -14,12 +14,18 @@ try:
 except:
     from ConfigParser import ConfigParser
 import itertools
-from urlparse import urlparse
+try:
+    from urllib.parse import urlparse, urlencode
+except ImportError:
+    from urlparse import urlparse
 from junit_xml import TestSuite, TestCase
 try:
     from cStringIO import StringIO
 except:
-    from StringIO import StringIO
+    try:
+        from StringIO import StringIO
+    except ImportError:
+        from io import StringIO
 import mock_decorators
 
 debug = False