Remove hardcoded python3.8 path

- Let the user overwrite Python binary name while calling make.

- Use environment variable set by make to instruct e2e_test.py which binary it
should call to execute Python code.

Makefile

@@ -1,7 +1,17 @@
-PYTHON = python3.8
-
+.POSIX:
 .PHONY: test unittest pre-clean clean
 
+#
+# On systems where Python 3.x binary has a different name, just
+# overwrite the name/path on the command line, like:
+#
+#     make test PYTHON=/usr/local/bin/python3.8
+#
+# This marco is passed via environment to test/e2e_test.py, where it's
+# used to compute further commands.
+#
+PYTHON = python3
+
 #
 # Run a set of end-to-end tests.
 #

test/e2e.ini

@@ -31,7 +31,6 @@ certs: test/certs
 [tests]
 # Number of "test-*" sections in this file, describing test cases.
 cases: 6
-python_path: /usr/local/bin/python3.8
 e2e_log: test/logs/e2e.log
 e2e_log_format: %(asctime)s %(pathname)s:%(lineno)d %(levelname)s [%(funcName)s] %(message)s
 e2e_log_datefmt: %Y-%m-%d %H:%M:%S

test/e2e_test.py

@@ -88,13 +88,15 @@ def execute_e2e_test(case_name, config, config_path):
     config file.  Each of these sections should contain
     following properties: 'descr', 'to', 'in' and 'out'.
     """
+    # This environment variable is set in Makefile.
+    python_path = os.getenv('PYTHON', 'python3')
 
     test_command = "GPG_MAILGATE_CONFIG=%s %s gpg-mailgate.py %s < %s" % (
         config_path,
-        config.get("tests", "python_path"),
+        python_path,
         config.get(case_name, "to"),
         config.get(case_name, "in"))
-    result_command = "%s %s %d" % (config.get("tests", "python_path"), config.get("relay", "script"), config.getint("relay", "port"))
+    result_command = "%s %s %d" % (python_path, config.get("relay", "script"), config.getint("relay", "port"))
 
     logging.debug("Spawning relay: '%s'" % (result_command))
     pipe = os.popen(result_command, 'r')