ORNL SANS: fix detector side masking

[Mathieu Doucet]

The ORNL SANS detector have two planes of tubes. There used to be an option to mask on of the two planes (front side or back side) but it no longer works. The problem is in the way the instrument parameters are accessed.

[Mathieu Doucet]

Re #7818 Fix masking issue

Changeset: f65894ada19b6981ea866a3cd1ec418479d13e7f

[Mathieu Doucet]

To Test: Execute the following script, click "Show Instrument", and see that the detector has zebra stripes where every second tube (along y-axis) is masked.

import mantid
from mantid.simpleapi import *
from reduction_workflow.instruments.sans.hfir_command_interface import *

BIOSANS()
SetSampleDetectorOffset(837.9)
SolidAngle(detector_tubes=True)
MonitorNormalization()
AzimuthalAverage(n_bins=100, n_subpix=1, log_binning=False)
NoIQxQy()
SetBeamCenter(96.7, 16.6)
NoSensitivityCorrection()
SetTransmission(1.0,0.0)
ThetaDependentTransmission(False)
AppendDataFile(["BioSANS_test_data.xml"])
NoSaveIq()
MaskDetectorSide('Back')
Reduce()

[Jay Rainey]

Now masks one of the two planes (producing zebra stripes). Easy to understand code.

Not sure why trac didn't auto update when I passed the ticket. Commit can be viewed ​github.

[Stuart Campbell]

This ticket has been transferred to github issue ​8663