Remove the usage of read_password from library files

The read_password function is defined inside stack.sh
and it cannot be used inside the "public library interface"
provided by DevStack.

Move the calls found inside library files to stack.sh,
following the same pattern of the other calls to read_password.

Change-Id: I8adc6723b677dfac2bef735f660e056c498bf773

lib/database

@@ -87,8 +87,6 @@ function initialize_database_backends {
 
     if [ -n "$MYSQL_PASSWORD" ]; then
         DATABASE_PASSWORD=$MYSQL_PASSWORD
-    else
-        read_password DATABASE_PASSWORD "ENTER A PASSWORD TO USE FOR THE DATABASE."
     fi
 
     # We configure Nova, Horizon, Glance and Keystone to use MySQL as their