Initialize CDS block data in es unit testing to avoid uninit var warnings from valgrind

[skliper]

Is your feature request related to a problem? Please describe.
Block data is used uninitialized in unit test:

cFE/modules/es/ut-coverage/es_UT.c

Line 4669 in c161cf0

uint8 BlockData[ES_UT_CDS_BLOCK_SIZE];

cFE/modules/es/ut-coverage/es_UT.c

Line 4789 in c161cf0

CFE_UtAssert_SUCCESS(CFE_ES_CopyToCDS(CDSHandle, &BlockData));

cFE/modules/es/ut-coverage/es_UT.c

Line 4795 in c161cf0

CFE_UtAssert_SUCCESS(CFE_ES_RestoreFromCDS(&BlockData, CDSHandle));

Describe the solution you'd like
Initialize.

Describe alternatives you've considered
None

Additional context
None

Requester Info
Jacob Hageman - NASA/GSFC