Returns MTBF summary for the given period. When assetId is an area/site, includes every
descendant asset's failure events rather than requiring a specific leaf asset.

---
### Parameters
**paramsDict** `Dictionary`<br />
<table class='dictionaryKeyTable'>
	<tbody>
 	<tr><td> - assetId</td><td>Integer</td><td>Not required  restricts to this asset and its descendants</td></tr>	
 	<tr><td> - endDate</td><td>DateTime</td><td>End date</td></tr>	
 	<tr><td> - startDate</td><td>DateTime</td><td>Start date</td></tr>	
	</tbody>
</table>

---
### Returns
**mtbfSummary** `pyDataset`<br />

---
### Example
```python
# Populate a plant-wide MTBF summary KPI tile for the current quarter
paramsDict = {
				'startDate': system.date.addDays(system.date.now(), -90),
				'endDate': system.date.now()
			}
data = system.kanoa.utilities.convertDatasetToJSON(system.kanoa.cmms.getMaintenanceMTBFSummary(paramsDict))

for i, row in enumerate(data):
	print 'Row %i'%i
	for k,v in row.items():
		print k,v
	
	break	#Just limiting to returning the columns from the first record for display purposes
>>> 
Row 0
MTBF_Days 14.0
MTBF_Minutes 20242.0
intervalCount 1
assetCount 1
failureCount 1
>>> 
```