Do not resolve config properties placeholders against environment variables by default

We have introduced automatic resolving of environment variables in case of using placeholder ${...} as a value of configuration property. This causes issues after upgrade especially in case of LDAP and server on Windows - Windows do have "username" env variable by default. In such case, username is resolved and breaks configuration of LDAP.

Placeholders should resolve only against other configuration properties values and environment variables with prefix "clover_".

If user wants to resolve environment variables, he/she has to use placeholder with "env:" prefix (eg. ${env:username} ).

For backward compatibility resolving of placeholders should properly process older style of escaping with double brackets ( $ username )