DMI bugfix modbus reconnect

[RyanZhaoXB]

fix the bug proposed in this issue: #98
add the Reconnect() function and reconnect to the device when the mapper fails to write data.
update the Get(), Set() and SetString function to GetWithRetry(), SetWithRetry() and SetStringWithRetry() function.

[kubeedge-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
To complete the pull request process, please assign kevin-wangzefeng after the PR has been reviewed.
You can assign the PR to them by writing /assign @kevin-wangzefeng in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[kubeedge-bot]

@RyanZhaoXB: PR needs rebase.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.