Retry logic for SSH connection in Cloud Server resource

There is a known issue with some Rackspace Cloud Server images where
they occasionally refuse SSH connections for a few seconds just after
becoming 'ACTIVE'.  This causes the stack creation to fail.

To avoid this, keep trying to initialize the SSH connection for up to 30
TaskRunner cycles.

Closes-Bug: #1287331
Change-Id: Icf28fb3c0de21cf733c4dd0d28a7b653af1bcd0b
Merge "Retry logic for SSH connection in Cloud Server resource"