Adds validation on creating batches so requests with
the read_length attribute will be forced to share the same value among the
batch that is being created
Adds a validation for supplying a number of requests fixed to 8 while
creating batches for the following pipelines:

- Cluster formation (old)
- Cluster formation SE
- Cluster formation PE
- Cluster formation PE (no controls)
- Cluster formation SE HiSeq
- Cluster formation SE HiSeq (no controls)
- Cluster formation SE (no controls)
- Cluster formation SE (spiked in controls)
- Cluster formation PE (spiked in controls)
- HiSeq Cluster formation PE (spiked in controls)
- Cluster formation SE HiSeq (spiked in controls)
Delegates validation of batch creation to batch.
Adds unit testing for batch validations in pipeline.
Adds migration for reading min_size of batch from database.
Refactors for is_read_length_consistent_for_batch
Moves changes to sequencing_pipeline instead of all pipelines.
Adds same validation for all pipelines.
Changes test unit for validation of sequencing pipelines for read_length.
Adds test unit for other pipelines to ignore this read_length validation.
Resolve merge conflicts
Merge branch 'emrojo-batch-validation-requests' into next_release