Fix process's output to stdout/stderr (MI)

Summary:
* Add CMIUtilString::Escape/Unescape methods (MI)
* Fix process's output to stdout/stderr (MI):
lldb-mi escapes process's output to show it in the following format:
```
~"..."
```

But previously not all characters were escaped by CMICmnLLDBDebuggerHandleEvents::ConvertPrintfCtrlCodeToString and output of
```
printf("'\n` - it's \\n\x12\"\\\"")
```
looked like:
```
~"'\r\n` - it's \n"\""
```

This patch fixes it by using CMIUtilString::Escape method and now it looks like:
```
~"'\r\n` - it's \\n\x12\"\\\""
```

Reviewers: abidh, emaste, clayborg

Reviewed By: clayborg

Subscribers: zturner, lldb-commits, emaste, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D7858

llvm-svn: 230652