Ensure that EPICS_DRIVER_PATH is set first

Previously, it was the case that running

$ iocsh -r module -l cellMods
$ iocsh -l cellMods -r module

would both work correctly, but if you looked at the IOC log it was not clear why that was the case; in the former case it appeared like we were finding the module before setting EPICS_DRIVER_PATH. This only worked because this variable is exported from the shell.

This change forces the -l flag to be processed before all of the other flags in order to ensure that paths are determined first.