Define the set of supported use cases for VirtualBox-based trials

I believe we should define a set of supported scenarios for the VirtualBox, update our scripts, update release notes and also quick start on Mirantis portal. At least to tell the users what they CAN and CANNOT do under VirtualBox (e.g. having a full-blown HA with Ceph is unrealistic even on 16GB laptop)

My suggestion is to introduce something along the lines of:
config_4GB.sh - non-HA, 1 controller, 1 compute
config_8GB.sh - non-HA, 1 controller, 3 compute nodes
config_16GB.sh - HA, 3 controllers, 1 compute

This is actually triggered by the latest discussion on fuel-dev.

>> Digging the issue with Galera, I found that our environments have very high RAM utilization which leads to the problem during environment deployment. For instance "HA deployment + neutron/GRE" requires almost 2.6-2.7 GB during deployment (corosync+mysql+puppet++rabbit+neutron+ovs+openstack services). I found high swap in/swap out usage during deployment with very high load average. This creates many sporadic issues with some services. They time out in random place making our debugging very hard. I would like to review our policy for CI environment and increase RAM (at least for bvt tests) to 3 GB.