The executor wrapper
l A global run defined as a sequence of local runs.
l A local run is an execution of the tool over a given src-
dest pair.
l A global run contains exactly one local run for every
src-dest pair.
l The state of a global run represents which src-dest
pairs have been tested so far (and which have not).
l Wrapper running at a given host starts the tool with the
correct destination basing on the state, and after
completion it updates the state and runs a new
wrapper on the next designated host with the new
state.