Tidy up options

Remove some unused options in avocado, add some new ones that do something, and fix the tagging issue with multiplexed tests. Now a multiplexed test looks a lot better:

    $ scripts/avocado run synctest --multiplex examples/tests/synctest.py.data/synctest.yaml 
    JOB ID    : 4d24b8ffb30aca5d4b49a98a88f4d731ec0fd590
    JOB LOG   : /home/lmr/avocado/job-results/job-2014-10-01T22.41-4d24b8f/job.log
    TESTS     : 9
    (1/9) synctest.py.short.short: PASS (5.23 s)
    (2/9) synctest.py.short.medium: PASS (2.27 s)
    (3/9) synctest.py.short.long: PASS (2.49 s)
    (4/9) synctest.py.medium.short: PASS (4.03 s)
    (5/9) synctest.py.medium.medium: PASS (3.14 s)
    (6/9) synctest.py.medium.long: PASS (2.40 s)
    (7/9) synctest.py.long.short: PASS (2.42 s)
    (8/9) synctest.py.long.medium: PASS (4.79 s)
    (9/9) synctest.py.long.long: PASS (4.44 s)
    PASS      : 9
    ERROR     : 0
    FAIL      : 0
    SKIP      : 0
    WARN      : 0
    NOT FOUND : 0
    TIME      : 31.22 s