iotile-ship should create a per recipe invocation temporary directory

Some steps will need to generate temporary files. There should be a single folder created for the recipe during execution to hold a separate folder for each step (created by `iotile-ship`, not the step) and then given to each step in its execution context parameter so that it can save temporary files there.

There should be a command line flag to determine whether this temporary directory is preserved after running iotile-ship or destroyed automatically