Bug 5008/some typos missed in rudder init and rudder upgrade adaptation

I explained this in the original Pull Request:

> I think we should use {ldapsearch,ldapmodrdn,ldapadd} from the PATH, not using the hardcoded /opt/rudder path. There are several reasons for that:
> 1) Future compatibility. PATH is a nice standard feature. Let's use it. We should, however, make sure at the beginning of the script that our PATH contains /opt/rudder/bin, just to be sure.
> 2) Availability. The ldap* tools under /opt/rudder get installed with the rudder-inventory-ldap package, which contains the LDAP server, and which won't be installed on a rudder-webapp node in a distributed architecture.
> 
> Therefore, we should also update the package dependencies to add a dependency on ldap-utils.