Remove prohibited characters from FAT16/32 labels (#755608)

GParted waits forever when attempting to set a FAT16/32 file system
label which contains prohibited characters [1][2].  This is because
mlabel asks a question and is waiting for input.  Force cancelling the
operation doesn't work either as GParted sends signal 2 (interrupt i.e.
[Ctrl-C]) but mtools commands specifically ignores this and a number of
other signals.  Have to kill mlabel with signal 9 (kill) to regain
control of GParted.

Mlabel command with prohibited characters in the label:

    # export MTOOLS_SKIP_CHECK=1
    # mlabel ::"MYLABEL/   " -i /dev/sdb10
    Long file name "MYLABEL/   " contains illegal character(s).
    a)utorename A)utorename-all r)ename R)ename-all
    s)kip S)kip-all q)uit (aArRsSq):

Remove prohibited characters from FAT16/32 file systems labels when
creating and labelling them.  Also upper case the label to meet label
requirements [1][2].  This silently corrects the label and the actual
label applied will be displayed when GParted refreshes after applying
the operation.

[1] Microsoft TechNet: Label
    https://technet.microsoft.com/en-us/library/bb490925.aspx

[2] Replicated in Wikikedia: label (command)
    https://en.wikipedia.org/wiki/Label_%28command%29

Bug 755608 - Labeling fat16/fat32 partitions hangs if certain characters
             included in label