Added try catch on write graph method in cpac_pipeline to bypass graph generation if dot is not installed
Added try catch on write graph method in cpac_pipeline to bypass graph generation if dot is not installed

sgiavasis/C-PAC,danlurie/C-PAC,sgiavasis/C-PAC,roijo/C-PAC_complexitytools,roijo/C-PAC_complexitytools,roijo/C-PAC_complexitytools,danlurie/C-PAC,sgiavasis/C-PAC,danlurie/C-PAC,sgiavasis/C-PAC,danlurie/C-PAC,roijo/C-PAC_complexitytools