Allow for tests to be disabled at runtime

Summary:
The current implementation of the test suite allows the user to run
a certain subset of tests using '-p', but does not allow the inverse,
where a user wants to run all but some number of known failing tests.
Implement this functionality.

Reviewers: labath, zturner, tfiala

Subscribers: jingham, sas, lldb-commits

Differential Revision: https://reviews.llvm.org/D24629

llvm-svn: 282298
diff --git a/lldb/packages/Python/lldbsuite/test/dotest_args.py b/lldb/packages/Python/lldbsuite/test/dotest_args.py
index 67fe9091..02d1047 100644
--- a/lldb/packages/Python/lldbsuite/test/dotest_args.py
+++ b/lldb/packages/Python/lldbsuite/test/dotest_args.py
@@ -96,6 +96,9 @@
         '-p',
         metavar='pattern',
         help='Specify a regexp filename pattern for inclusion in the test suite')
+    group.add_argument('--excluded', metavar='exclusion-file', help=textwrap.dedent(
+        '''Specify a file for tests to exclude. File should contain lists of regular expressions for test files or methods,
+                                with each list under a matching header (xfail files, xfail methods, skip files, skip methods)'''))
     group.add_argument(
         '-G',
         '--category',