build: reject merge conflict checkin attempts

Although attempts to build code containing merge conflict markers
USUALLY results in compile errors, this patch adds an explicit check
for the conflict end marker.

If for some unknown reason it's necessary to check in the text
'>>>>>>>', construct it by concatenation: ">>>"">>>>"
or '>>>' + '>>>>' depending on the language involved.

Type: improvement

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: Iaad2aa8b87a71137a3bb9a09f7f4159909bf79ab

build-root/scripts/checkstyle.sh

@@ -72,6 +72,11 @@ cd ${VPP_DIR}
 git status
 for i in ${FILELIST}; do
     if [ -f ${i} ] && [ ${i} != "build-root/scripts/checkstyle.sh" ] && [ ${i} != "extras/emacs/fix-coding-style.el" ]; then
+        grep -q '>>>>>>>' ${i}
+        if [ $? == 0 ]; then
+            echo "Unresolved merge conflict detected in" ${i} "... Abort."
+            exit 1
+        fi
         grep -q "fd.io coding-style-patch-verification: ON" ${i}
         if [ $? == 0 ]; then
             EXTENSION=`basename ${i} | sed 's/^\w\+.//'`