Export the execution summary to file

[smithfarm]

If one runs "ceph-salt apply" and then "expand all", one gets a summary, in the form of a tree, of what actions were performed on each minion. This is very nice - bravo!

However, when the user leaves the ncurses interface, this detailed execution summary disappears forever. There is a log file with lots of details in it, but it would be nice to also save ("export") the execution summary as a separate file.

NOTE: this would probably also require a supportutils patch to ensure that the file containing the exported execution summary is included in the supportconfig tarball.