Use context name instead of key_uuid

Use context name instead of key_uuid

context.key_uuid is only used as a suffix for the key files.
There is already a unique ID associated with a the context;
the context name includes a task ID, which is a UUID.

This patch sets context.key_uuid to to context.name instead of
generating a separate UUID

As a result, get_short_key_uuid() is not needed.

JIRA: YARDSTICK-1028
Change-Id: Id175061d6cfe23a068bb3d12ce176c1f176e8236
Signed-off-by: Emma Foley <emma.l.foley@intel.com>