Add `filename` property
Add `filename` property

The spring data loader/generator now supports reading data from files [1].
Hence the `filename` setting was introduced. perfrunner now also needs
to supply this setting.

This commit can be merged without any harm before the spring change is
merged.

[1]: https://github.com/couchbaselabs/spring/pull/4

Change-Id: I8985b445a34bcc2934bc110cc86c2c2ab5e70060
Reviewed-on: http://review.couchbase.org/49064
Reviewed-by: Venu Uppalapati <5c73d43f38c8de2bc4a2e4d15365e52f60b59dae@gmail.com>
Tested-by: Venu Uppalapati <5c73d43f38c8de2bc4a2e4d15365e52f60b59dae@gmail.com>

couchbase/perfrunner,hsharsha/perfrunner,mikewied/perfrunner,thomas-couchbase/perfrunner,EricACooper/perfrunner,dkao-cb/perfrunner,EricACooper/perfrunner,thomas-couchbase/perfrunner,EricACooper/perfrunner,EricACooper/perfrunner,mikewied/perfrunner,pavel-paulau/perfrunner,couchbase/perfrunner,vmx/perfrunner,couchbase/perfrunner,vmx/perfrunner,pavel-paulau/perfrunner,pavel-paulau/perfrunner,hsharsha/perfrunner,couchbase/perfrunner,pavel-paulau/perfrunner,couchbase/perfrunner,couchbase/perfrunner,PaintScratcher/perfrunner,PaintScratcher/perfrunner,dkao-cb/perfrunner,pavel-paulau/perfrunner