reindex() does not reindex a MultiIndex
#### Code Sample, a copy-pastable example if possible

```python
df = pd.DataFrame.from_dict({'A': {(42, 'foo', 4): 0, (42, 'foo', 9): 0},
 'B': {(42, 'foo', 4): 0, (42, 'foo', 9): 0},
 'C': {(42, 'foo', 4): 0, (42, 'foo', 9): 0},
 'D': {(42, 'foo', 4): 0, (42, 'foo', 9): 0},
 'E': {(42, 'foo', 4): 0, (42, 'foo', 9): 0},
 'F': {(42, 'foo', 4): 0, (42, 'foo', 9): 0},
 'G': {(42, 'foo', 4): 1, (42, 'foo', 9): 1}})

print(df.reindex(pd.RangeIndex(-1, 11), level=2, fill_value=0))
```

Output:

```
          A  B  C  D  E  F  G
42 foo 4  0  0  0  0  0  0  1
       9  0  0  0  0  0  0  1
```

#### Problem description

I would expect that the resulting dataframe have 12 rows, with indices `(42, 'foo', i)` for `i` from `-1` to `10`.

Apologies if I am just misunderstanding something. I haven't managed to find any information in the docs on the reason for the current behavior.

#### Output of ``pd.show_versions()``

<details>

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.4.final.0
python-bits: 64
OS: Linux
OS-release: 4.14.24-1-MANJARO
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.22.0
pytest: None
pip: 9.0.1
setuptools: 38.5.1
Cython: 0.27.3
numpy: 1.14.0
scipy: 1.0.0
pyarrow: None
xarray: None
IPython: 6.2.1
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2018.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.1.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 1.0.1
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
```

</details>
