Create MaxScale directories

If the installation directory is something else than /usr,
then the directories

    <install-dir>/var/cache/maxscale
    <install-dir>/var/log/maxscale
    <install-dir>/var/run/maxscale

will be created at installation time.

CMakeLists.txt

@@ -357,3 +357,11 @@ if(PACKAGE)
   message(STATUS "You can install startup scripts and system configuration files for MaxScale by running the 'postinst' shell script located at ${CMAKE_INSTALL_PREFIX}.")
   message(STATUS "To remove these installed files, run the 'postrm' shell script located in the same folder.")
 endif()
+
+# NOTE: If you make changes here, ensure they are compatible with the
+#       situation in gwdirs.h.in.
+if (NOT CMAKE_INSTALL_PREFIX EQUAL "/usr")
+  install(DIRECTORY DESTINATION var/cache/maxscale)
+  install(DIRECTORY DESTINATION var/log/maxscale)
+  install(DIRECTORY DESTINATION var/run/maxscale)
+endif()

server/include/gwdirs.h.in

@@ -21,6 +21,8 @@
 
 EXTERN_C_BLOCK_BEGIN
 
+// NOTE: If you make changes here, ensure they are compatible with the
+//       situation in <root>/CMakeLists.txt, where directories are installed.
 #define MXS_DEFAULT_PID_SUBPATH    "run/maxscale"
 #define MXS_DEFAULT_LOG_SUBPATH    "log/maxscale"
 #define MXS_DEFAULT_DATA_SUBPATH   "lib/maxscale"