[TestBase.runCmd] Better error message when runCmd fails.

Summary:
Before:
    AssertionError: False is not True : Process is launched successfully

After:
    AssertionError: False is not True : Command 'run a.out' failed.
    >>> error: invalid target, create a target using the 'target create' command
    >>> Process could not be launched successfully

Reviewers: clayborg

Reviewed By: clayborg

Subscribers: lldb-commits, vharron

Differential Revision: http://reviews.llvm.org/D9948

llvm-svn: 238363

lldb/test/functionalities/data-formatter/refpointer-recursion/TestDataFormatterRefPtrRecursion.py

@@ -37,7 +37,7 @@ class DataFormatterRefPtrRecursionTestCase(TestBase):
 
         lldbutil.run_break_set_by_file_and_line (self, "main.cpp", self.line, num_expected_locations=1, loc_exact=True)
 
-        self.runCmd("run", RUN_SUCCEEDED)
+        self.runCmd("run", RUN_FAILED)
 
         # The stop reason of the thread should be breakpoint.
         self.expect("thread list", STOPPED_DUE_TO_BREAKPOINT,