Enhance the non-root installer script

Enhance the non-root installer script to do the following:

• Determine if Couchbase Server is installed or not.
• If it's not installed, do a non-root install of the rpm package.
• If Couchbase Server is already installed, check to see if the package file (RPM etc) -
• is a newer version than what is installed.
• If the package version is the same, do nothing.
• If the package version is newer, do a non-root upgrade with this new package file.
• If the package version is older than the installed version raise an error