history transition should be able to save the graph to a file

[krig]

From https://bugzilla.suse.com/show_bug.cgi?id=927475

Transition usage:

transition [<number>|<index>|<file>] [nograph] [v...] [scores] [actions] [utilization]
transition showdot [<number>|<index>|<file>]
transition log [<number>|<index>|<file>]
transition save [<number>|<index>|<file> [name]]

Without a subcommand the local pengine is used to calculate and show the graph.

Subcommand showdot displays the .dot file delivered with the report.

graph usage (which shows the configuration of the PE):

graph <pe> [<gtype> [<file> [<img_format>]]]

Perhaps sth like:

transition graph [<number>|<index>|<file>] [<gtype> [<file> [<img_format>]]]

Or to extend showdot (graph is already used hence may cause confusion):

transition showdot [<number>|<index>|<file>] [<file> [<img_format>]]

In the latter case we'd need to default to the local pengine to provide the graph if there's no dot file in the report.