Replace 'person_reid_msg_ptr_' with 'person_reid_topic_' [issue #125]

[Corsair-cxs]

fix #125
What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the dev-2020.3 branch for ros_openvino_toolkit, not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature

Other information:

[LewisLiuPub]

• please don't add postfix "_ptr" to a pointer parameter.
• please follow the naming convension for class parameters. e.g. xxx_msg_ptr --> xxx_topic.