no need for fetch, handle failed backports

git/githelpers

@@ -111,7 +111,15 @@ backport_pr() {
     fi
 
     echo Backporting ${PR} to ${BRANCH} from ${REMOTE}
-    git fetch ${REMOTE} pull/${1}/head:pr/${1}
-    git checkout ${BRANCH} && curl -s "https://github.com/elastic/kibana/pull/${PR}.patch" | git am
+    git checkout ${BRANCH} && git pull ${REMOTE} ${BRANCH} && curl -s "https://github.com/elastic/kibana/pull/${PR}.patch" | git am
+
+    # if the backport couldn't be cleanly applied, tell the user and exit
+    if [ $? -ne 0 ]; then
+        echo "FAILED - Backport could not be cleanly applied!"
+        echo "FAILED - Fix by hand or run 'git am --abort'"
+        exit 2
+    fi
+
+    # switch back if we didn't start in the target branch
     [ "$THISBRANCH" != "$BRANCH" ] && git checkout -
 }