Fix handling of the executable arg which contains spaces (MI)

* Don't use the CMICmdArgValFile::GetFileNamePath for the CMIDriver::m_strCmdLineArgExecuteableFileNamePath
  because it wraps path with spaces into quotes what is already being done in CMIDriver::LocalDebugSessionStartupExecuteCommands
* Improve the MiSyntaxTestCase.test_lldbmi_specialchars test to catch this error
  ```
    $ bin/lldb-mi "~/p/ hello"
    (gdb)
    -file-exec-and-symbols "\"~/p/ hello\""
    ^error,msg="Command 'file-exec-and-symbols'. Target binary '\"~/p/ hello\"' is invalid. error: unable to find executable for '/"~/p/ hello/"'"
  ```

llvm-svn: 234888