test: add Browser.cmd()
test: add Browser.cmd()

Add a new method to Browser that returns the full command & arguments
needed to run a browser; the implementations are moved from
CDP.browser_cmd().

martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit