Missing test cases for software bus API parameter/return combinations

[jphickey]

Is your feature request related to a problem? Please describe.
The following parameter/return code combinations are not exercised by the software bus functional test:

 + condition: CFE_SB_CreatePipe[any]=>CFE_SB_MAX_PIPES_MET
 + condition: CFE_SB_DeletePipe[CFE_SB_PipeId_t@0]=>ERROR_RESOURCEID_INVALID
 + condition: CFE_SB_GetPipeIdByName[<null-pointer>@1]=>ERROR_NULL_POINTER
 + condition: CFE_SB_MessageStringGet[<null-pointer>@0]=>ERROR_NULL_POINTER
 + condition: CFE_SB_MessageStringGet[<null-pointer>@1]=>ERROR_NULL_POINTER
 + condition: CFE_SB_MessageStringSet[<null-pointer>@0]=>ERROR_NULL_POINTER
 + condition: CFE_SB_MessageStringSet[<null-pointer>@1]=>ERROR_NULL_POINTER
 + condition: CFE_SB_ReceiveBuffer[any]=>CFE_SB_NO_MESSAGE
 + condition: CFE_SB_ReceiveBuffer[any]=>CFE_SB_PIPE_RD_ERR
 + condition: CFE_SB_Subscribe[any]=>CFE_SB_BUF_ALOC_ERR
 + condition: CFE_SB_Subscribe[any]=>CFE_SB_MAX_DESTS_MET
 + condition: CFE_SB_Subscribe[any]=>CFE_SB_MAX_MSGS_MET
 + condition: CFE_SB_SubscribeEx[any]=>CFE_SB_BUF_ALOC_ERR
 + condition: CFE_SB_SubscribeEx[any]=>CFE_SB_MAX_DESTS_MET
 + condition: CFE_SB_SubscribeEx[any]=>CFE_SB_MAX_MSGS_MET
 + condition: CFE_SB_SubscribeLocal[any]=>CFE_SB_BUF_ALOC_ERR
 + condition: CFE_SB_SubscribeLocal[any]=>CFE_SB_MAX_DESTS_MET
 + condition: CFE_SB_SubscribeLocal[any]=>CFE_SB_MAX_MSGS_MET
 + condition: CFE_SB_TransmitBuffer[any]=>CFE_SB_MSG_TOO_BIG
 + condition: CFE_SB_TransmitMsg[any]=>CFE_SB_BUF_ALOC_ERR
 + condition: CFE_SB_Unsubscribe[any]=>CFE_SB_INTERNAL_ERR
 + condition: CFE_SB_UnsubscribeLocal[any]=>CFE_SB_INTERNAL_ERR

Describe the solution you'd like
Solve each missing case in one of three ways:

1. Add a test case covering that option
2. Update the API documentation
3. Add a @covtest tag if the combination can only be reasonably achieved in a coverage environment

Additional context
Part of/related to #1724 (each subsystem will be handled separately)

Requester Info
Joseph Hickey, Vantage Systems, Inc.