Update generate-greenplum-path.sh for upgrade package

Following the [Greenplum Server RPM Packaging Specification][0], we need
to update greenplum_path.sh file, and ensure many environment variables
set correct.

There are a few basic requirments for Greenplum Path Layer:

* greenplum-path.sh shall be installed to `${installation
  prefix}/greenplum-db-[package-version]/greenplum_path.sh`
* ${GPHOME} is set by given parameter, by default it should point to
  `%{installation prefix}/greenplum-db-devel`
* `${LD_LIBRARY_PATH}` shall be safely set to avoid a trailing colon
  (which will cause the linker to search the current directory when
  resolving shared objects)
* `${PYTHONHOME}` shall be set to `${GPHOME}/ext/python`
* `${PYTHONPATH}` shall be set to `${GPHOME}/lib/python`
* `${PATH}` shall be set to `${GPHOME}/bin:${PYTHONHOME}/bin:${PATH}`
* If the file `${GPHOME}/etc/openssl.cnf` exists then `${OPENSSL_CONF}`
  shall be set to `${GPHOME}/etc/openssl.cnf`
* The greenplum_path.sh file shall pass [ShellCheck][1]

[0]: https://github.com/greenplum-db/greenplum-database-release/blob/master/Greenplum-Server-RPM-Packaging-Specification.md#detailed-package-behavior
[1]: https://github.com/koalaman/shellcheckCo-authored-by: NTingfang Bao <bbao@pivotal.io>
Co-authored-by: NXin Zhang <zhxin@vmware.com>
Co-authored-by: NNing Wu <ningw@vmware.com>
Co-authored-by: NShaoqi Bai <bshaoqi@vmware.com>

gpMgmt/bin/generate-greenplum-path.sh

 #!/usr/bin/env bash
 
-if [ x$1 != x ] ; then
-    GPHOME_PATH=$1
-else
-    GPHOME_PATH="\`pwd\`"
+if [ -z "$1" ]; then
+  printf "Must specify a value for GPHOME"
+  exit 1
 fi
 
-if [ "$2" = "ISO" ] ; then
-	cat <<-EOF
-		if [ "\${BASH_SOURCE:0:1}" == "/" ]
-		then
-		    GPHOME=\`dirname "\$BASH_SOURCE"\`
-		else
-		    GPHOME=\`pwd\`/\`dirname "\$BASH_SOURCE"\`
-		fi
-	EOF
-else
-	cat <<-EOF
-		GPHOME=${GPHOME_PATH}
-	EOF
-fi
+GPHOME_PATH="$1"
+cat <<EOF
+GPHOME="${GPHOME_PATH}"
 
+EOF
 
 PLAT=`uname -s`
 if [ $? -ne 0 ] ; then
@@ -28,78 +17,28 @@ if [ $? -ne 0 ] ; then
     exit 1
 fi
 
-cat << EOF
-
-# Replace with symlink path if it is present and correct
-if [ -h \${GPHOME}/../greenplum-db ]; then
-    GPHOME_BY_SYMLINK=\`(cd \${GPHOME}/../greenplum-db/ && pwd -P)\`
-    if [ x"\${GPHOME_BY_SYMLINK}" = x"\${GPHOME}" ]; then
-        GPHOME=\`(cd \${GPHOME}/../greenplum-db/ && pwd -L)\`/.
-    fi
-    unset GPHOME_BY_SYMLINK
-fi
-EOF
-
-cat <<EOF
-#setup PYTHONHOME
-if [ -x \$GPHOME/ext/python/bin/python ]; then
-    PYTHONHOME="\$GPHOME/ext/python"
-    export PYTHONHOME
-fi
-EOF
-
-#setup PYTHONPATH
-if [ "x${PYTHONPATH}" == "x" ]; then
-    PYTHONPATH="\$GPHOME/lib/python"
-else
-    PYTHONPATH="\$GPHOME/lib/python:${PYTHONPATH}"
-fi
-cat <<EOF
-PYTHONPATH=${PYTHONPATH}
-EOF
-
-GP_BIN_PATH=\$GPHOME/bin
-GP_LIB_PATH=\$GPHOME/lib
-
-if [ -n "$PYTHONHOME" ]; then
-    GP_BIN_PATH=${GP_BIN_PATH}:\$PYTHONHOME/bin
-    GP_LIB_PATH=${GP_LIB_PATH}:\$PYTHONHOME/lib
-fi
-cat <<EOF
-PATH=${GP_BIN_PATH}:\$PATH
-EOF
-
-cat <<EOF
-LD_LIBRARY_PATH=${GP_LIB_PATH}:\${LD_LIBRARY_PATH-}
-export LD_LIBRARY_PATH
-EOF
-
 # AIX uses yet another library path variable
 # Also, Python on AIX requires special copies of some libraries.  Hence, lib/pware.
 if [ "${PLAT}" = "AIX" ]; then
-cat <<EOF
-PYTHONPATH=\${GPHOME}/ext/python/lib/python2.7:\${PYTHONPATH}
-LIBPATH=\${GPHOME}/lib/pware:\${GPHOME}/lib:\${GPHOME}/ext/python/lib:/usr/lib/threads:\${LIBPATH}
+cat <<"EOF"
+PYTHONPATH="${GPHOME}/ext/python/lib/python2.7:${PYTHONPATH}"
+LIBPATH="${GPHOME}/lib/pware:${GPHOME}/lib:${GPHOME}/ext/python/lib:/usr/lib/threads:${LIBPATH}"
 export LIBPATH
-GP_LIBPATH_FOR_PYTHON=\${GPHOME}/lib/pware
+GP_LIBPATH_FOR_PYTHON="${GPHOME}/lib/pware"
 export GP_LIBPATH_FOR_PYTHON
 EOF
 fi
 
-# openssl configuration file path
-cat <<EOF
-if [ -e \$GPHOME/etc/openssl.cnf ]; then
-OPENSSL_CONF=\$GPHOME/etc/openssl.cnf
-export OPENSSL_CONF
+cat <<"EOF"
+
+if [ -e "$GPHOME/etc/openssl.cnf" ]; then
+	OPENSSL_CONF="$GPHOME/etc/openssl.cnf"
 fi
-EOF
 
-cat <<EOF
 export GPHOME
 export PATH
-EOF
-
-cat <<EOF
+export PYTHONHOME
 export PYTHONPATH
+export LD_LIBRARY_PATH
+export OPENSSL_CONF
 EOF
-