More tests for lr_url_substitute()
More tests for lr_url_substitute()

Adds tests for substitution syntax with braces.
Adds tests for variable which name is prefix of other variable.
Removes tests for substitutions of variable without name.

rpm-software-management/librepo,Tojaj/librepo,Tojaj/librepo,Tojaj/librepo,rpm-software-management/librepo,rpm-software-management/librepo