tools: tc-testing: Can refer to $TESTID in test spec

When processing the commands in the test cases, substitute
the test id for $TESTID.  This helps to make more flexible
tests.  For example, the testid can be given as a command
line argument.

As an example, if we wish to save the test output to a file
named for the test case, we can write in the test case:

"cmdUnderTest": "some test command | tee -a $TESTID.out"
Signed-off-by: Brenda J. Butler <bjb@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/tc-testing/tdc.py

@@ -177,6 +177,7 @@ def prepare_env(args, pm, stage, prefix, cmdlist, output = None):
                 '"{}" did not complete successfully'.format(prefix))
 
 def run_one_test(pm, args, index, tidx):
+    global NAMES
     result = True
     tresult = ""
     tap = ""
@@ -184,6 +185,9 @@ def run_one_test(pm, args, index, tidx):
         print("\t====================\n=====> ", end="")
     print("Test " + tidx["id"] + ": " + tidx["name"])
 
+    # populate NAMES with TESTID for this test
+    NAMES['TESTID'] = tidx['id']
+
     pm.call_pre_case(index, tidx['id'])
     prepare_env(args, pm, 'setup', "-----> prepare stage", tidx["setup"])
 
@@ -227,6 +231,8 @@ def run_one_test(pm, args, index, tidx):
 
     index += 1
 
+    # remove TESTID from NAMES
+    del(NAMES['TESTID'])
     return tap
 
 def test_runner(pm, args, filtered_tests):