[RFE] Intelligent Volume Expand by adding subvolumes

[aravindavk]

PR #1281(Issue #852) adds support for Volume expand by expanding the bricks. When distribute count is not given or given more than the existing value then we need to expand the volume by adding more sub volumes.

• Collect expand size as API input
• Get existing sub volume size
• if expand size > sub volume size, then number_of_new_subvols = ceil(expand_size / subvol_size)
• Number of new bricks required = num_bricks_in_existing_subvol * number_of_new_subvols
• Expand defaults based on existing sub volumes(File system type, replica count, disperse count etc)
• Plan brick layout based on above information
• Reuse the prepare bricks transaction steps
• Reuse the Volume expand Transaction steps

[atinmu]

Not within the new MVP of GCS/1.0