Support constraints on job instances (probably by making instance_definition configurable)

[mboldt]

We have a tile that requires the number of instances of a job to be exactly 1. The instance count is currently hardcoded to be configurable in tile-generator

tile-generator/tile_generator/tile_metadata.py

Lines 594 to 606 in bef5bab

	instance_def = {
	'configurable': True,
	'default': job.get('instances', 1),
	'name': 'instances',
	'type': 'integer'
	}
	if job.get('singleton') or job.get('lifecycle') == 'errand':
	instance_def['configurable'] = False
	instance_def['default'] = 1
	if self.config['metadata_version'] < 1.7:
	bosh_release_job['instance_definitions'] = [instance_def]
	else:
	bosh_release_job['instance_definition'] = instance_def

We should probably just expose the instance_definintion as something the tile author can set.

[cf-gitbot]

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