Implement new methods for handling an error in MI commands.

Summary:
The new methods take SBError object and call handler,
specified by user, depending on SBError status.

Reviewers: aprantl, clayborg, labath

Reviewed By: aprantl, clayborg

Subscribers: ki.stfu, lldb-commits

Differential Revision: https://reviews.llvm.org/D48295

llvm-svn: 335541