mtplot: clickclear option to toggle clearing on click

Sometimes you don't want the screen to clear on click. With this
change, you can tap 'c' or use a command line arg.

BUG=chromium-os:32964
TEST=tested on device w/ both toggle key and short/long command line
args

Change-Id: I75564c2277282408c807e4beafde036515715f19
Reviewed-on: https://gerrit.chromium.org/gerrit/28435
Reviewed-by: Daniel Kurtz <[email protected]>
Tested-by: Andrew de los Reyes <[email protected]>
Commit-Ready: Andrew de los Reyes <[email protected]>
1 file changed