add ctest support and remove absolute path from etc directory

Some packagers use ctest by default to run tests. This is a small
easy-win to add to biboumi. In addition some distros don't use /etc as
their configuration path, and have to patch this out (see guix and nix),
so this is also an easy fix.

CMakeLists.txt

@@ -293,6 +293,9 @@ endforeach()
 find_package(Catch2)
 if(Catch2_FOUND)
   target_link_libraries(test_suite Catch2::Catch2WithMain)
+  include(CTest)
+  include(Catch)
+  catch_discover_tests(test_suite)
 endif()
 
 #
@@ -339,7 +342,7 @@ install(TARGETS ${PROJECT_NAME} RUNTIME                     DESTINATION bin)
 install(FILES   ${CMAKE_CURRENT_BINARY_DIR}/man/biboumi.1   DESTINATION share/man/man1         OPTIONAL COMPONENT documentation)
 install(FILES   ${CMAKE_CURRENT_BINARY_DIR}/biboumi.service DESTINATION lib/systemd/system     COMPONENT init)
 file(GLOB policy_files conf/*policy.txt)
-install(FILES   ${policy_files}                             DESTINATION /etc/biboumi           COMPONENT configuration)
+install(FILES   ${policy_files}                             DESTINATION etc/biboumi           COMPONENT configuration)
 
 #
 ## Dist target