On Ubuntu check for graphviz system config
On Ubuntu check for graphviz system config

- Sometimes it seems Ubuntu doesn't always set up the Graphviz
  handler config. If it's missing, generate it.

Change-Id: I2c1e566817de8415f8b360c6f967cd76307a2a52
Signed-off-by: Chris Luke <77b9dc41542bba50ff94234985ac7feef3984b39@flirble.org>

FDio/vpp,GabrielGanne/vpp-flowtable,GabrielGanne/vpp-flowtable,vpp-dev/vpp,chrisy/vpp,vpp-dev/vpp,milanlenco/vpp,FDio/vpp,GabrielGanne/vpp-flowtable,GabrielGanne/vpp-flowtable,FDio/vpp,FDio/vpp,milanlenco/vpp,vpp-dev/vpp,vpp-dev/vpp,GabrielGanne/vpp-flowtable,milanlenco/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,GabrielGanne/vpp-flowtable,FDio/vpp,milanlenco/vpp,vpp-dev/vpp,milanlenco/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,milanlenco/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp