Return nothing from Put Cache Entry in CMC

[alex-chew]

See awslabs/aws-encryption-sdk-specification#194.

Current implementation:

aws-encryption-sdk-java/src/main/java/com/amazonaws/encryptionsdk/caching/CryptoMaterialsCache.java

Lines 43 to 60 in 8f5f69e

	/**
	* Attempts to add a new entry to the encrypt cache to be returned on subsequent
	* {@link #getEntryForEncrypt(byte[], UsageStats)} calls.
	*
	* In the event that an error occurs when adding the entry to the cache, this function shall still return a
	* EncryptCacheEntry instance, which shall act as if the cache entry was immediately evicted and/or invalidated.
	*
	* @param cacheId The identifier for the item in the cache
	* @param encryptionMaterials The {@link EncryptionMaterials} to associate with this new entry
	* @param initialUsage The initial usage stats for the cache entry
	* @return A new, locked EncryptCacheEntry instance containing the given encryptionMaterials
	*/
	EncryptCacheEntry putEntryForEncrypt(
	byte[] cacheId,
	EncryptionMaterials encryptionMaterials,
	CacheHint hint,
	UsageStats initialUsage
	);

[lavaleri]

We are pursuing another mechanism to ensure that the implementation meets the specification.