Add environment variable WITH_DEB to control if buill.sh should generate .deb file

paddle/scripts/docker/build.sh

@@ -81,7 +81,7 @@ fi
 # PaddlePaddle.  This awkwardness is due to
 # https://github.com/PaddlePaddle/Paddle/issues/1854.  It also
 # describes a solution.
-if [[ ${WITH_DOC} == "ON" ]]; then
+if [[ ${WITH_DOC:-OFF} == "ON" ]]; then
     cat <<EOF
 ========================================
 Building documentation ...
@@ -125,6 +125,7 @@ fi
 
 # generate deb package for current build
 # FIXME(typhoonzero): should we remove paddle/scripts/deb ?
+if [[ ${WITH_DEB:-OFF} == "ON" ]]; then
     cat <<EOF
 ========================================
 Generating .deb package ...
@@ -139,6 +140,8 @@ if [ ${err_code} -ne 0 ]; then
         exit ${err_code}
     fi
     set -e
+fi
+
 cat <<EOF
 ========================================
 Generate /paddle/build/Dockerfile ...