#14 Make LoadKeyByUUID atomic WRT TCS

[Kent Yoder]

Right now, a LoadKeyByUUID is done by calling
TCS_LoadKeyByUUID and then calling
TCS_GetRegisteredKeyBlob. Inbetween the 2 operations,
another app could unregister the key, causing the
operation to fail.

Change the code to call GetRegisteredKeyBlob first,
then load by blob, which would make the TSP op atomic
WRT TCS PS.