Add tests for MemcacheD storage backend (#362)

_Also_:
* Added background `renderd` process testing
* Added `renderd` section without `stats_file` testing
* Added `render_*` via TCP tests
* Added `render_* --verbose`  tests
* Added `render_expired --delete-from` tests
* Added `render_expired --no-progress` tests
* Added `render_expired --touch-from` tests
* Added `PARAMETERIZE_STYPE=language` map configuration testing
* Added `HTCPHOST`/`HOST` map configuration testing

docker/ubuntu/Dockerfile

@@ -27,7 +27,8 @@ RUN --mount=id=ubuntu:${ubuntu_version}-/var/cache/apt,sharing=locked,target=/va
         libiniparser-dev \
         libmapnik-dev \
         libmemcached-dev \
-        librados-dev
+        librados-dev \
+        netbase
 
 ## Build, Test & Install `mod_tile`
 COPY . /tmp/mod_tile_src