Add dataclean target.
Add dataclean target.

This just cleans up your data without deleting compile output.

Change-Id: I1537dc0d4c90b0b9cf04c4048e281293df39d82e
Reviewed-on: http://review.membase.org/4520
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

nimishzynga/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,daverigby/ns_server,ceejatec/ns_server,daverigby/ns_server,daverigby/ns_server,daverigby/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,membase/ns_server,mschoch/ns_server,vzasade/ns_server,daverigby/ns_server,membase/ns_server,nimishzynga/ns_server,ceejatec/ns_server,mschoch/ns_server,vzasade/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,vzasade/ns_server,membase/ns_server,ceejatec/ns_server,nimishzynga/ns_server,membase/ns_server,nimishzynga/ns_server,ceejatec/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,vzasade/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,membase/ns_server,ceejatec/ns_server,nimishzynga/ns_server,membase/ns_server,pavel-blagodov/ns_server