Change implementation of default test_dir for TestStatus

For some reason, some tests in scripts_regression_tests were failing for me with
the old version of this code - maybe because default arguments are evaluated
when the function is defined (not when it is called)?

This new version seems more likely to be what's wanted - i.e., getting the
current working directory at the time when the function is called, not the time
when it's defined.

From a quick look, it looks like this default could be removed entirely and made
a required argument.

Test suite: None
Test baseline: N/A
Test namelist changes: N/A
Test status: N/A

Fixes: None

User interface changes?: No

Code review: None

utils/python/CIME/test_status.py

@@ -62,7 +62,14 @@ def _test_helper2(file_contents, wait_for_run=False, check_throughput=False, che
 
 class TestStatus(object):
 
-    def __init__(self, test_dir=os.getcwd(), test_name=None):
+    def __init__(self, test_dir=None, test_name=None):
+        """
+        Create a TestStatus object
+
+        If test_dir is not specified, it is set to the current working directory
+        """
+        if test_dir is None:
+            test_dir = os.getcwd()
         self._filename = os.path.join(test_dir, TEST_STATUS_FILENAME)
         self._phase_statuses = OrderedDict() # {name -> (status, comments)}
         self._test_name = test_name