xlabel disappears in scatter plots with subplots and colorbar
This is related to this PR https://github.com/pandas-dev/pandas/pull/20446. Separating the subplot and single plots into two issues.

Copying from https://github.com/pandas-dev/pandas/pull/20446:

```
def make_multiplots(numrows=2,numcols=2,sharey=True,sharex=True,PATCH_MODE_FLAG = True, is_scatter = True):
    fig, axes = pl.subplots(numrows,numcols,sharey=sharey,sharex=sharex )
    for i in range(axes.shape[0]):
        for j in range(axes.shape[1]):
            random_array = np.random.random((1000,3))
            df = pd.DataFrame(random_array,columns=['A label','B label','C label'])
            if is_scatter:
                df.plot.scatter('A label','B label',c='C label', PATCH_MODE_FLAG = PATCH_MODE_FLAG,ax=axes[i,j]);
            else:
                df.plot.hexbin('A label','B label',gridsize=20, PATCH_MODE_FLAG = PATCH_MODE_FLAG,ax=axes[i,j]);
            
            
make_multiplots(numrows=2,numcols=2,sharey=True, sharex=True, PATCH_MODE_FLAG = False, is_scatter=True);pl.suptitle('pandas current version');            
make_multiplots(numrows=2,numcols=2,sharey=True, sharex=True, PATCH_MODE_FLAG = True, is_scatter=True);pl.suptitle('patch fixing x-axis');            
make_multiplots(numrows=2,numcols=2,sharey=True, sharex=True, PATCH_MODE_FLAG = False, is_scatter=False);pl.suptitle('pandas current version');            
make_multiplots(numrows=2,numcols=2,sharey=True, sharex=True, PATCH_MODE_FLAG = True, is_scatter=False);pl.suptitle('patch fixing x-axis');  
```          
![image](https://user-images.githubusercontent.com/26352146/37773292-97f0a5a2-2db3-11e8-9912-8f2f558f5740.png)
![image](https://user-images.githubusercontent.com/26352146/37773303-9eaa8e08-2db3-11e8-975b-ce454a33e277.png)
![image](https://user-images.githubusercontent.com/26352146/37773312-a30c9b62-2db3-11e8-9040-864b16ebf59a.png)
![image](https://user-images.githubusercontent.com/26352146/37773316-a6259916-2db3-11e8-9be2-592295972768.png)
