Always append gpg_agent_script to .bashrc

[penguian]

The gadi-cylc-setup script adds module commands to the end of ~/.bashrc. These commands include the boilerplate that mosrs.setup.gpg_startup searches for. The result is that mosrs-setup inserts its changes to ~/.bashrc in the middle of the changes made by gadi-cylc-setup. Instead of doing this, mosrs.setup.gpg_startup should simply append to ~/.bashrc. This also simplifies the script.