Parse command lines of existing jobs more robustly

[ericaltendorf]

E.g.:

$ ./plotman.py interactive
Warning: unrecognized args: -k32 -n1
Warning: unrecognized args: -t/tmp -2/tmp2
Warning: unrecognized args: -d/dst -b6000
Warning: unrecognized args: -u128 -r3
...

Should probably use a standard library for parsing the args. :)