Workflow for creating line features between two coordinate pairs in QGIS

The Points2One Plugin might be helpful here. Your data will have to be in the following format:

id,      order, x,       y
stream1, 1,     x_start, y_start
stream1, 2,     x_end,   y_end
stream2, 1,     x_start, y_start
stream2, 2,     x_end,   y_end

After loading a file like this, you should get four points displayed. In Points2One Plugin, you can chose that points should be connected to lines grouped by the "id" value and sorted by the "order" value.

In QGIS, try the "Points2One" plugin, and set the output geometry to lines. It requires the features you wish to be grouped together to have the same IDs.

EDIT: I see you have the data in a table. You would need to first import the table to a point shapefile (using the Delimited Text plugin). Then use the shapefile in the Points2One plugin.

Kosmo GIS also has a tool for this - "Get Lines From Points".

With QGIS >3.0 (where Points2One is not avilable) you can do this without any plugin, using Toolbox > Points to path.