If runfetchcmd() fails with bb.process.NotFoundError, the message output
is simply "Fetch command" which doesn't really explain what the problem
is.
Add "not found" to clarify what happened.
(Bitbake rev: 8de9dc02ed6a73b47f2ab10be30d1aed7954bc72)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>