[DOCKER] Small fixes in docker startup scripts

docker/db/wait_for_db.sh

@@ -11,7 +11,7 @@ case $DBMS in
         exit 1
 esac
 
-while ! $CMD;
+while ! eval $CMD;
 do
     echo "Waiting for DB..."
     sleep 3

docker/social/install.sh

@@ -6,7 +6,7 @@ case "${DBMS}" in
         DB_EXISTS=$?
         ;;
     'mariadb')
-        mysqlcheck -cqs -uroot -p"${MYSQL_ROOT_PASSWORD}" -hdb social 2> /dev/null
+        mysqlcheck -cqs -uroot -p"${MYSQL_ROOT_PASSWORD}" -hdb ${SOCIAL_DB} 2> /dev/null
         DB_EXISTS=$?
         exit 1
         ;;