Simple example gets stuck

For me this simple example tries two random values for `f` and then gets stuck always retrying the same value.
Not sure if bug in Labwatch or in RoBO.

``` python
from sacred import Experiment
from labwatch import LabAssistant
from labwatch.hyperparameters import UniformInt
from labwatch.optimizers import BayesianOptimization

ex = Experiment()
la = LabAssistant(ex, database_name='labwatch_demo2',
optimizer=BayesianOptimization)

@ex.config
def cfg():
f = 42

@la.searchspace
def small_search_space():
f = UniformInt(lower=32, upper=64, default=32)

@ex.automain
def run(f):
return f
```

Like this:
```
(labwatch) greff@Liz:~/Programming/labwatch/examples$ python my_example.py -p -d with small_search_space
WARNING: SMAC not found
Configuration (modified, added, typechanged, doc):
f = 61
seed = 862826954 # the random seed for this experiment
-------------------------------------------------------------------------------
INFO - my_example - Running command 'run'
INFO - my_example - Started run with ID "1"
INFO - my_example - Result: 61
INFO - my_example - Completed after 0:00:00
(labwatch) greff@Liz:~/Programming/labwatch/examples$ python my_example.py -p -d with small_search_space
WARNING: SMAC not found
Configuration (modified, added, typechanged, doc):
f = 52
seed = 674124630 # the random seed for this experiment
-------------------------------------------------------------------------------
INFO - my_example - Running command 'run'
INFO - my_example - Started run with ID "2"
INFO - my_example - Result: 52
INFO - my_example - Completed after 0:00:00
(labwatch) greff@Liz:~/Programming/labwatch/examples$ python my_example.py -p -d with small_search_space
WARNING: SMAC not found
Configuration (modified, added, typechanged, doc):
f = 52
seed = 886589901 # the random seed for this experiment
-------------------------------------------------------------------------------
INFO - my_example - Running command 'run'
INFO - my_example - Started run with ID "3"
INFO - my_example - Result: 52
INFO - my_example - Completed after 0:00:00
(labwatch) greff@Liz:~/Programming/labwatch/examples$ python my_example.py -p -d with small_search_space
WARNING: SMAC not found
Configuration (modified, added, typechanged, doc):
f = 52
seed = 614908786 # the random seed for this experiment
-------------------------------------------------------------------------------
INFO - my_example - Running command 'run'
INFO - my_example - Started run with ID "4"
INFO - my_example - Result: 52
INFO - my_example - Completed after 0:00:00
```