[lldb-mi] Fix implementation for a few mi commands

Summary:
Some of the mi commands implemented in lldb-mi are incomplete/not confirming to the spec.
- `gdb-show` and `gdb-set` doesn't support getting/setting `disassembly-flavor`
- `environment-cd` should also change the working directory for inferior
- debugger CLI output should be printed as console-stream-output record, rather than being dumped directly
to stdout
- `target-select` should provide inner error message in mi response

Related bug report:
- https://llvm.org/bugs/show_bug.cgi?id=28026
- https://llvm.org/bugs/show_bug.cgi?id=28718
- https://llvm.org/bugs/show_bug.cgi?id=30265

Reviewers: ki.stfu, abidh

Subscribers: abidh, ki.stfu, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D24711

llvm-svn: 291104