Fixing ssh bug leading to crash. (ATLASJT-409)

Solution for ATLASJT-409. A crash occurs when tier-0 reprocessing on the grid attempts to make ssh connection to aiatlas, to which it does not have access. Made changes to base_data* (4 python files). Rather than assigning server name and splitting by commas immediately, a check is done to see if an empty string was passed. This allows bypassing of the ssh step without changing the tier-0 wrapper or affecting any other behavior.