SFrame serialization in job truncates column name

```
import graphlab as gl
sf = gl.SFrame({'a   ': 1})
sf2 = gl.deploy.job.create(lambda x: sf, x=0).get_results()
assert sf2.column_names()[0] == 'a' # Succeeds but should fail
assert sf2.column_names()[0] == 'a   ' # Fails but should succeed
```
