Library need to check and handle the case if parent devfile is with a different schema version

[yangcao77]

Which area/kind this issue is related to?

/area library

Issue Description

As we discussed in the meeting, library should check parent devfile's schema version before overriding/merging.
For a parent devfile with higher schema version: error out directly.
For a parent devfile with lower schema version: take it and merge, since devfile is expected to be backward compatible .