Re #10784. Removing links annd regular files.
Re #10784. Correct install_prefix.
Fix template filename for generated post_uninstall rpm scriptlet

Refs #10784
Fix RPM scriptlets to cope with upgrading a package.

The RPM mechanism doesn't allow you to distinguish between an install and
an upgrade so we check for the existence of a file to see if it was
an upgrade.
Refs #10784
Merge pull request #106 from mantidproject/bugfix/10784_linux_startup_scripts

Re #10784. Removing links and regular files.