bash-completion: handle comma-separated options

bash-completion: handle comma-separated options

This solution can become messy when you have too many options listed,
because it repeats all of them. For example, after invoking completion
with this input:

    $ partx --output END,SECTORS,SCHEME,START,

You got these completions:

    END,SECTORS,SCHEME,START,FLAGS,  END,SECTORS,SCHEME,START,NR,
    END,SECTORS,SCHEME,START,TYPE,
    END,SECTORS,SCHEME,START,NAME,   END,SECTORS,SCHEME,START,SIZE,
    END,SECTORS,SCHEME,START,UUID,

Nevertheless, it works even with numbers (listed options properly
excluded from completion). Try to invoke completion after
'chcpu --disable ' or 'lsblk --exclude ' to see it in action.

Few issues remained:

    * completion interrupts after encountering ':' in listed option,
    like in 'MAJ:MIN' in lsblk, losetup.
    * lscpu completion is broken: it inserts space after '--extended',
    but lscpu assumes there is no space after this option. It also
    doesn't complete '--parse' option.
    * some completion options are outdated (for example, lscpu MMHZ). We
    need to sync them with code. Fix for lscpu follows.

Signed-off-by: Boris Egorov <egorov@linux.com>