Switch gdalbuildvrt command to subprocess.call()
Switch gdalbuildvrt command to subprocess.call()

os.system() can be a bit limited, such as when dealing with
*lots* of tiles and fail silently due to subshell issues.
subprocess.call() (with shell=False) is better at this and
fails with more understandable messages if needed.

ScottMcMichael/StereoPipeline,ScottMcMichael/StereoPipeline,oleg-alexandrov/StereoPipeline,oleg-alexandrov/StereoPipeline,NeoGeographyToolkit/StereoPipeline,oleg-alexandrov/StereoPipeline,NeoGeographyToolkit/StereoPipeline,ScottMcMichael/StereoPipeline,ScottMcMichael/StereoPipeline,NeoGeographyToolkit/StereoPipeline,ScottMcMichael/StereoPipeline,oleg-alexandrov/StereoPipeline,oleg-alexandrov/StereoPipeline,NeoGeographyToolkit/StereoPipeline,ScottMcMichael/StereoPipeline,oleg-alexandrov/StereoPipeline,NeoGeographyToolkit/StereoPipeline,NeoGeographyToolkit/StereoPipeline