When an index build fails due to running out of disk space, it will cause the node to crash. We should attempt to handle this more gracefully.

If we get an ENOSPC from WiredTiger, we should drop any storage engine tables and external sort files immediately and then write an abortIndexBuild oplog entry to cancel the index build.

Alternatively, we could:

• Proactively cancel the index build if we expect that we won't have any disk space to complete the index build
• Expose metrics about expected disk space requirements and allow administrators to cancel index builds that are expected to exceed this limit.