Fix -break-insert for system functions (MI)

Summary:
# Fix -break-insert for system functions
# Fix MiExecTestCase to use -break-insert instead of CLI "b"
# Improve MiBreakTestCase: now it uses printf() instead of in-house function

All tests pass on OS X.

Test Plan:
```
$ bin/lldb-mi --interpreter
(gdb)
-file-exec-and-symbols ~/p/hello
^done
(gdb)
=shlibs-added,shlib-info=[num="1",name="hello",dyld-addr="-",reason="dyld",path="/Users/IliaK/p/hello",loaded_addr="-",dsym-objpath="/Users/IliaK/p/hello.dSYM/Contents/Resources/DWARF/hello"]
-break-insert -f printf
^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0xffffffff",func="??",file="??",fullname="??/??",line="0",pending=["printf"],times="0",original-location="printf"}
(gdb)
=breakpoint-modified,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0xffffffff",func="??",file="??",fullname="??/??",line="0",pending=["printf"],times="0",original-location="printf"}
-exec-run
^running
...
*stopped,reason="breakpoint-hit",disp="del",bkptno="1",frame={addr="0x7fff8a476910",func="printf",args=[],file="??",fullname="??",line="-1"},thread-id="1",stopped-threads="all"
(gdb)
```

Reviewers: abidh, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D8412

llvm-svn: 232734