fail only when wasn't found any python

tests/test.mk

@@ -81,10 +81,10 @@ ifdef RUBY_GEM_VERSION
 	@chmod a+x ./$(BIN_PATH)/tests/rubythemis_test.sh
 	@$(PRINT_OK_)
 endif
-ifdef PYTHON_VERSION
+ifdef PYTHON2_VERSION
 	@echo -n "make tests for pythemis "
 	@echo "#!/bin/bash -e" > ./$(BIN_PATH)/tests/pythemis_test.sh
-	@echo "python -m unittest discover -s tests/pythemis" >> ./$(BIN_PATH)/tests/pythemis_test.sh
+	@echo "python2 -m unittest discover -s tests/pythemis" >> ./$(BIN_PATH)/tests/pythemis_test.sh
 ifdef PYTHON3_VERSION
 	@echo "echo Python3 $(PYTHON3_VERSION) tests" >> ./$(BIN_PATH)/tests/pythemis_test.sh
 	@echo "python3 -m unittest discover -s tests/pythemis" >> ./$(BIN_PATH)/tests/pythemis_test.sh
@@ -137,13 +137,17 @@ ifdef PHP_VERSION
 endif
 
 test_python:
-ifdef PYTHON_VERSION
+# run test if any of python version available
+ifneq ($(or $(PYTHON2_VERSION),$(PYTHON3_VERSION)),)
 	@echo "------------------------------------------------------------"
 	@echo "Running pythemis tests."
 	@echo "If any error, check https://github.com/cossacklabs/themis/wiki/Python-Howto"
 	@echo "------------------------------------------------------------"
 	$(TEST_BIN_PATH)/pythemis_test.sh
 	@echo "------------------------------------------------------------"
+else
+	@echo "python2 or python3 not found"
+	@exit 1
 endif
 
 test_ruby: