Update the expected match string.

o lldbtest.py:

  Indicate when a command fails, even if there is nothing in the error stream.

o TestHelp.py:

  Add a regression test case for 'help image dump symtab'.

o CommandObjectHelp.cpp:

  Some of the logic branches with successful help command results were not tagged
  with a Success Status.  They are fixed now.  This is important for Python
  interaction.

llvm-svn: 116062