Fix evaluation commands (MI)

Summary:
These changes include:
* Fix -var-create to be able use current frame '*' (MI)
* Fix print-values option in -var-update (MI)
* Fix 'variable doesn't exist' error in -var-show-attributes (MI)
* Mark print-values option as 'handled-by-cmd' in -var-update (MI)
* Fix SBValue::GetValueDidChange if value was changed
* Fix lldb-mi: -data-evaluate-expression shows undef vars. Before this fix -data-evaluate-expression perceives undefined variables as strings:
```
(gdb)
-data-evaluate-expression undef
^done,value="undef"
```
* Minor fix: -data-evaluate-expression uses IsUnknownValue()
* Enable MiEvaluateTestCase test

All test pass on OS X.

Reviewers: abidh, clayborg

Subscribers: lldb-commits, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D7463

llvm-svn: 228414