[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
diff --git a/lldb/test/lang/cpp/static_members/TestCPPStaticMembers.py b/lldb/test/lang/cpp/static_members/TestCPPStaticMembers.py
index 83516b7..8dae233 100644
--- a/lldb/test/lang/cpp/static_members/TestCPPStaticMembers.py
+++ b/lldb/test/lang/cpp/static_members/TestCPPStaticMembers.py
@@ -37,7 +37,7 @@
         self.set_breakpoint(line_number('main.cpp', '// breakpoint 1'))
         self.set_breakpoint(line_number('main.cpp', '// breakpoint 2'))
 
-        self.runCmd("process launch", RUN_SUCCEEDED)
+        self.runCmd("process launch", RUN_FAILED)
         self.expect("expression my_a.access()",
                     startstr = "(long) $0 = 10")