Issue with job executable and argument when using a storage plugin

[jannisspeer]

The method format_job_exec(job), which is called in the run_job() method of the Executor object, returns a string which also contains a pip install statement when using a storage plugin. This case is not handled currently. I tested this with the xrootd storage plugin.

[jannisspeer]

Could we drop this pip install and just assume that the storage plugin is installed on the job nodes?