test: enable passing wildcards with path to test runner

Currently, passing wildcard testname args to the test runner from outside the `test/functional/` directory does not work. See this recent IRC discussion for more background: http://www.erisian.com.au/bitcoin-core-dev/log-2019-07-10.html#l-262 (lines 262 to 323).

This small change enables passing multiple wildcards with paths, as long as the paths are coherent. Examples:
  - test/functional/test_runner.py test/functional/wallet*
  - functional/test_runner.py functional/wallet*
  - test/functional/test_runner.py ./test/functional/tool* test/functional/mempool*

A current limitation that this PR does not change: 9 test files with arguments in their name are not picked up by wildcard search.

- Squashed commit: non-mutating version

- Squashed commit: minor code optimisation

Author: jonatack

test/functional/test_runner.py

@@ -269,11 +269,22 @@ def main():
     test_list = []
     if tests:
         # Individual tests have been specified. Run specified tests that exist
-        # in the ALL_SCRIPTS list. Accept the name with or without .py extension.
-        tests = [test + ".py" if ".py" not in test else test for test in tests]
+        # in the ALL_SCRIPTS list. Accept names with or without a .py extension.
+        # Specified tests can contain wildcards, but in that case the supplied
+        # paths should be coherent, e.g. the same path as that provided to call
+        # test_runner.py. Examples:
+        #   `test/functional/test_runner.py test/functional/wallet*`
+        #   `test/functional/test_runner.py ./test/functional/wallet*`
+        #   `test_runner.py wallet*`
+        #   but not:
+        #   `test/functional/test_runner.py wallet*`
+        # Multiple wildcards can be passed:
+        #   `test_runner.py tool* mempool*`
         for test in tests:
-            if test in ALL_SCRIPTS:
-                test_list.append(test)
+            script = test.split("/")[-1]
+            script = script + ".py" if ".py" not in script else script
+            if script in ALL_SCRIPTS:
+                test_list.append(script)
             else:
                 print("{}WARNING!{} Test '{}' not found in full test list.".format(BOLD[1], BOLD[0], test))
     elif args.extended: