HPCC-8528 Add #!/bin/bash in install scripts

Add #!/bin/bash in pre/post install/uninstall scripts.
Most Linux will tolerate if this is missing. But some old distro
for example, Ubuntu 10.04 will fail and throw an error during install/uninstall

clienttools/install/postinst.in

@@ -1 +1,2 @@
+#!/bin/bash
 ${CMAKE_INSTALL_PREFIX}/etc/init.d/install/post_install.sh 

clienttools/install/postrm.in

@@ -1,3 +1,4 @@
+#!/bin/bash
 CLIENT_TOOLS_BASE=${PREFIX}/${DIR_NAME}/${version}
 if [ -e "$CLIENT_TOOLS_BASE" ] &&  [ -n $(ls -A $CLIENT_TOOLS_BASE) ]  
 then

clienttools/install/prerm.in

@@ -1 +1,2 @@
+#!/bin/bash
 ${CMAKE_INSTALL_PREFIX}/etc/init.d/install/post_install.sh -u