Implement a function that returns an error to replace existing uses of
the IsOSSupported utility, where callers had to produce the error after
checking.
The IsOSSupported function was used in combination with images, so implementing
a utility in "image" to prevent having to import pkg/system (which contains many
unrelated functions)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
