LU-553 build: improve checks for commit-msg Improve the checks done by the commit-msg script. It now ensures that all the parts of the commit message are present. - validate that the Change-Id: generated from 'git hash-object' is not empty, since this can happen if git is unhappy with the options - check for only one Change-Id: line (multiple Signed-off-by: OK) - describe the "component:" field better, with examples If there was an error committing the message, save a copy to a temporary file, so that it can be edited and re-used, instead of having to recreate it each time, or fetch it from .git/COMMIT_MSG. Signed-off-by: Joe