CMake: remove hardcoded CMAKECONFIG_INSTALL_DIR path

Currently this path is hardcoded to lib/cmake.
Some distributions have different library path (like lib64).
So reuse LIB_INSTALL_DIR for that to make CMAKECONFIG_INSTALL_DIR
configurable and usable in such distros.
Signed-off-by: Ruslan Bilovol <rbilovol@cisco.com>

CMakeLists.txt

@@ -199,9 +199,9 @@ CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/${PROJECT_NAME}ConfigVersion.cmake.in
     ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake @ONLY)
 
 # ... for the install tree
-SET( CMAKECONFIG_INSTALL_DIR lib/cmake/${PROJECT_NAME} )
+SET( CMAKECONFIG_INSTALL_DIR ${LIB_INSTALL_DIR}/cmake/${PROJECT_NAME} )
 FILE( RELATIVE_PATH REL_INCLUDE_DIR
-    "${CMAKE_INSTALL_PREFIX}/${CMAKECONFIG_INSTALL_DIR}"
+    "${CMAKECONFIG_INSTALL_DIR}"
     "${CMAKE_INSTALL_PREFIX}/include" )
 
 SET( ${PROJECT_NAME}_INCLUDE_DIR "\${${PROJECT_NAME}_CMAKE_DIR}/${REL_INCLUDE_DIR}" )