Fix log file generation in lldb-mi.

When it runs, lldb-mi creates a log file. There is an option --noLog
to disable the creation but it does not work and you end up with log 
file. This happens as log is enabled in a few places in the code 
although it has been disabled by this option.

This commit tried to fix the problem in the following way.

Log file generation is disabled by default.
You can enable it by giving --log option. It is the only way to enable
it. Rest of the call have been removed.

So the code basically remove the calls that enable the log 
unconditionally and changes the option --noLog to --log.

llvm-svn: 227810