Avoid overwrite of the error message in AbortFn

The AbortFn() used to overwrite the error message, hiding the real
failure reported in ErrorAbort(). And we will miss the failure in
the script patterns like 'blockimageupdate() || abort()'

We will ensure there's one line break at the end of ErrorAbort's
error message; and append to the existing error message when calling
abort().

Test: Message from ErrorAbort shows up in the log
Change-Id: I3aebd06629c5129330250c7fe5e8cdead2ae85bc