script: add overlayfs setup script for chaindata (#599)

overlayfs can used to quickly rollback all the changes we make to the chaindata
when testing.

Example usage:

> pwd
/home/test

> ls
chaindata

> overlayfs_chaindata.sh -d /home/test
+ cd /home/test/
+ mkdir -p upper
+ mkdir -p workdir
+ mv chaindata orig_chaindata
+ mkdir -p chaindata
+ mount -t overlay overlay -olowerdir=./orig_chaindata,upperdir=./upper,workdir=./workdir chaindata

\# make changes to chaindata
...

\# rollback to original chaindata
> overlayfs_chaindata.sh -d /home/test -c
+ cd /home/minh_bui_skymavis_com/
+ umount ./chaindata
+ rm -rf chaindata
+ rm -rf upper
+ rm -rf workdir
+ mv orig_chaindata chaindata

script/overlayfs_chaindata.sh

@@ -0,0 +1,73 @@
+#!/bin/bash
+
+# A tool to create/clean up the overlayfs over the chaindata directory.
+# overlayfs can be used to quickly rollback the chaindata directory
+# after testing.
+
+unset DATADIR
+unset CLEANUP
+
+PROGNAME=$(basename "$0")
+USAGE="$PROGNAME -d datadir [-c]
+
+where:
+    -d datadir: the chaindata's parent directory
+    -c:         clean up mode
+"
+
+while getopts :hd:c option; do
+  case $option in
+    h)
+      echo "$USAGE"
+      exit 0
+      ;;
+    d) DATADIR=$OPTARG ;;
+    c) CLEANUP=true ;;
+    :)
+      echo "$PROGNAME: option requires an argument -- '$OPTARG'" >&2
+      exit 1
+      ;;
+    *)
+      echo "$PROGNAME: bad option -$OPTARG" >&2
+      echo "Try '$PROGNAME -h' for more information" >&2
+      exit 1
+      ;;
+  esac
+done
+shift $((OPTIND - 1))
+
+if [[ -z $DATADIR ]]; then
+  echo "$PROGNAME: missing mandatory option" >&2
+  echo "Try '$(basename "$0") -h' for more information" >&2
+  exit 1
+fi
+
+cleanup_overlay () {
+  set -ex
+
+  cd $DATADIR
+  umount ./chaindata
+  rm -rf chaindata
+  rm -rf upper
+  rm -rf workdir
+  mv orig_chaindata chaindata
+}
+
+setup_overlay () {
+  set -ex
+
+  cd $DATADIR
+  mkdir -p upper
+  mkdir -p workdir
+  mv chaindata orig_chaindata
+  mkdir -p chaindata
+
+  mount -t overlay overlay \
+    -olowerdir=./orig_chaindata,upperdir=./upper,workdir=./workdir chaindata
+}
+
+if [[ "$CLEANUP" = "true" ]]; then
+  cleanup_overlay
+else
+  setup_overlay
+fi