Link against Connector-C.

Now, qc_mysqlembedded is linked against MySQL's embedded library,
and MaxScale itself against Connector-C.

So, in order to build MaxScale, Connector-C must be installed.
This has been tested with Connector-C 2.2.1.

The build variable MYSQLCLIENT_LIBRARIES is no longer used.

query_classifier/test/CMakeLists.txt

@@ -1,3 +1,9 @@
+subdirs(MYSQL_DIR_ALL ${MYSQL_DIR})
+foreach(DIR ${MYSQL_DIR_ALL})
+  include_directories(${DIR})
+endforeach()
+include_directories(${MYSQL_INCLUDE})
+
 if(${ERRMSG} MATCHES "ERRMSG-NOTFOUND")
   message(FATAL_ERROR "The errmsg.sys file was not found, please define the path with -DERRMSG=<path>")
 else()