We remove the requirement for rt-app to run on a rooted device as this
does not appear to be required. We make sure that we run the workload
from a directory where we have write permissions by first changing the
directory before executing the workload (in_directory argument of
invoke).
In the case that the device is rooted, we run rt-app as
root. Otherwise, we simply run the workload.
By default rt-app writes to stderr, not to stdout. Therefore, if we
only sample the stdout, we get no output from the workload itself.
With this change, we redirect stderr to stdout to allow us to get the
workload output.
