VMware: update the default 'task_poll_interval' time

The original means that each operation against the backend takes at
least 5 seconds. The default is updated to 0.5 seconds.

DocImpact
    Updated default value for task_poll_interval from 5 seconds to
    0.5 seconds

Change-Id: I867b913f52b67fa9d655f58a2e316b8fd1624426
Closes-bug: #1274439
Merge "VMware: update the default 'task_poll_interval' time"