Installation of cmake files to prefix set at installation time does not work

[roe85]

Describe the bug When installing rmqcpp with cmake --install . --prefix some/dir everything is installed to some/dir except for the cmake files

To Reproduce Steps to reproduce the behavior:

1. After building rmqcpp go to build folder
2. Call cmake --install . --prefix /tmp/b
3. See error because it tries to install the *.cmake files to /usr, the others work

Expected behavior It adheres to the prefix also for the *.cmake files

Environment (please complete the following information):

• Linux