CMSDK : Fix generateAlertColorFromDrawable for non BitmapDrawable

In the case that the bitmap being passed in was not a bitmap drawable,
we were not retaining any of the attributes from the original drawable.
This patch ensures we ask that drawable to draw on the canvas/bitmap so we
can use that information. Also add tests around it.

Change-Id: I3eefba6e6624fe0bed4965ddf9029320c40f7420