Update Prepare.sh in centos CI branch

The script accepts three command-line arguments:

reference to the latest pr [optional]
working directory	   [optional]
git repository	           [optional]

Sample usage:
./prepare.sh --gitrepo=https://github.com/example --workdir=opt/build --ref=pull/123/head

Fixes: #968

Signed-off-by: Yug Gupta <ygupta@redhat.com>

prepare.sh

@@ -1,7 +1,65 @@
 #!/bin/sh
 
+# In case no value is specified, default values will be used.
+gitrepo="https://github.com/ceph/ceph-csi"
+workdir="tip/"
+ref="master"
+
+ARGUMENT_LIST=(
+    "ref"
+    "workdir"
+    "gitrepo"
+)
+
+opts=$(getopt \
+    --longoptions "$(printf "%s:," "${ARGUMENT_LIST[@]}")help" \
+    --name "$(basename "${0}")" \
+    --options "" \
+    -- "$@"
+)
+
+eval set -- ${opts}
+
+while true; do
+    case "${1}" in
+    --help)  
+        shift
+        echo "Options:"
+        echo "--help|-h                 specify the flags"
+        echo "--ref                     specify the reference of pr"
+        echo "--workdir                 specify the working directory"
+        echo "--gitrepo                 specify the git repository" 
+        echo " "
+        echo "Sample Usage:"
+        echo "./prepare.sh --gitrepo=https://github.com/example --workdir=/opt/build --ref=pull/123/head"
+        exit 0
+        ;;
+    --gitrepo)  
+        shift
+        gitrepo=${1}
+        ;;
+    --workdir)  
+        shift
+        workdir=${1}
+        ;;
+    --ref)  
+        shift
+        ref=${1}
+        echo ${ref}      
+        ;;
+    --)
+        shift
+        break
+        ;;
+    esac
+    shift
+done
+
 set -x
 
 yum -y install git podman
 
-git clone --single-branch --branch=master https://github.com/ceph/ceph-csi /opt/build
+git clone --depth=1 ${gitrepo} ${workdir}
+cd ${workdir}
+git fetch --depth=1 origin "${ref}:tip/${ref}"
+git checkout "tip/${ref}"