tests: Add migration dirty-limit capability test

tests: Add migration dirty-limit capability test

Add migration dirty-limit capability test if kernel support
dirty ring.

Migration dirty-limit capability introduce dirty limit
capability, two parameters: x-vcpu-dirty-limit-period and
vcpu-dirty-limit are introduced to implement the live
migration with dirty limit.

The test case does the following things:
1. start src, dst vm and enable dirty-limit capability
2. start migrate and set cancel it to check if dirty limit
   stop working.
3. restart dst vm
4. start migrate and enable dirty-limit capability
5. check if migration satisfy the convergence condition
   during pre-switchover phase.

Note that this test case involves many passes, so it runs
in slow mode only.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <e55a302df9da7dbc00ad825f47f57c1a756d303e.1698847223.git.yong.huang@smartx.com>