passenger: Use opt_prefix

Cleaning up places that can use `opt_prefix` instead of
`#{HOMEBREW_PREFIX}/opt/<packagename>`

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
chruby: Use opt_prefix

Cleaning up places that can use `opt_prefix` instead of
`#{HOMEBREW_PREFIX}/opt/<packagename>`

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
nexus: Use opt_prefix

Cleaning up places that can use `opt_prefix` instead of
`#{HOMEBREW_PREFIX}/opt/<packagename>`

This package had a hardcoded `/usr/local/` instead of a
Homebrew path in the .plist file.

Closes #22079.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>