Added robot tests for MEC028.

MEC028/WAI/AP_INFO/WaiApInfo.robot

MEC028/WAI/AP_INFO/environment/variables.txt

MEC028/WAI/AP_INFO/schemas/ApInfo.schema.json

MEC028/WAI/AP_INFO/schemas/ProblemDetails.schema.json

MEC028/WAI/EXT_SUB/ExistingSubscription.robot

MEC028/WAI/EXT_SUB/environment/variables.txt

MEC028/WAI/EXT_SUB/jsons/UpdateAssocStaSubscription.json

MEC028/WAI/EXT_SUB/jsons/UpdateAssocStaSubscription_BR.json

MEC028/WAI/EXT_SUB/schemas/AssocStaSubscription.schema.json

MEC028/WAI/STA_INFO/WaiStaInfo.robot

MEC028/WAI/STA_INFO/environment/variables.txt

MEC028/WAI/STA_INFO/schemas/ProblemDetails.schema.json

MEC028/WAI/STA_INFO/schemas/StaInfo.schema.json

MEC028/WAI/SUB/WaiSubscription.robot

MEC028/WAI/SUB/environment/variables.txt

MEC028/WAI/SUB/jsons/AssocStaSubscription.json

MEC028/WAI/SUB/jsons/AssocStaSubscription_BR.json

MEC028/WAI/SUB/schemas/AssocStaSubscription.schema.json

MEC028/WAI/SUB/schemas/SubscriptionLinkList.schema.json

MEC028/outputs/log-20210506-145611.html