Adding validation to the ansicolor plugin

Adding validation that the supplied value is one that is
supported and added a default if no colormap is supplied.  Is
there anything I should do to make the ansicolor and colormap
names be more in line with the current coding standard?  I.e.
allow colormap for backwards compatibility but also color-map
to follow the current standard.

Change-Id: Ibf673e6fe32bcfed32991baf886fe3afc6bafd01