[virtualbox] Default memory limit for second and third nodes

[Vladimir Sharshov]

Problem:

For second and third nodes we setup limit 1GB, but any multi roles (for example cinder) with HA controllers require at least 1536+ MB (2048+ MB recommended). If we try to deploy cluster (controller + cinder), we got puppet fail with memory errors.

Precondition:

- UI suggested HA as default for cluster;
- in our documentation we suggest create nodes with 1536+ MB (2048+ MB recommended) for VirtualBox;
- also in documentation we recommend HA configurations (2048+ MB per controller).

Solution:

Remove vm_slave_memory_mb[2] and vm_slave_memory_mb[3] from config.sh. This nodes will use default value which now equals to 1536 MB.

vm_slave_memory_mb[1]=2048
vm_slave_memory_mb[2]=1024 # for compute node 1GB is recommended, otherwise VM instances in OpenStack may not boot
vm_slave_memory_mb[3]=1024 # for dedicated Cinder, 768Mb is OK, but Ceph needs 1Gb minimum