Include mariadb-connector-c as a subproject

This is how the MariaDB server does it and this is how MaxScale should
do it as well. This also makes it much easier to include the source code
in a source tarball as CPack will do this for submodules but won't do it
for projects added via ExternalProject_Add.

Author: markus456

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "mariadb-connector-c"]
+	path = mariadb-connector-c
+	url = https://github.com/MariaDB/mariadb-connector-c.git

BUILD/build_deb_local.sh

@@ -7,6 +7,8 @@ set -x
 
 cd ./MaxScale
 
+git submodule update --init
+
 NCPU=$(grep -c processor /proc/cpuinfo)
 
 if [ "$PARALLEL_BUILD" == "no" ]

BUILD/build_rpm_local.sh

@@ -7,6 +7,8 @@ set -x
 
 cd ./MaxScale
 
+git submodule update --init
+
 NCPU=$(grep -c processor /proc/cpuinfo)
 
 if [ "$PARALLEL_BUILD" == "no" ]

cmake/BuildMariaDBConnector.cmake

@@ -5,17 +5,8 @@
 # sets the variables set by FindMariaDBConnector.cmake so that it appears that
 # the system has the connector.
 
-set(MARIADB_CONNECTOR_C_REPO "https://github.com/MariaDB/mariadb-connector-c.git"
-  CACHE STRING "MariaDB Connector-C Git repository")
-
-# Connector-C tag to use
-set(MARIADB_CONNECTOR_C_TAG "v3.2.5"
-  CACHE STRING "MariaDB Connector-C Git tag")
-
 ExternalProject_Add(connector-c
-  GIT_REPOSITORY ${MARIADB_CONNECTOR_C_REPO}
-  GIT_TAG ${MARIADB_CONNECTOR_C_TAG}
-  GIT_SHALLOW TRUE
+  SOURCE_DIR ${CMAKE_SOURCE_DIR}/mariadb-connector-c/
   CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}/connector-c/install -DWITH_UNIT_TESTS=N -DWITH_CURL=N -DWITH_EXTERNAL_ZLIB=Y
   BINARY_DIR ${CMAKE_BINARY_DIR}/connector-c
   INSTALL_DIR ${CMAKE_BINARY_DIR}/connector-c/install