Relax LazyDataObject.augmentations() implementation

Relax LazyDataObject.augmentations() implementation

We use double-checked locking to guard against concurrent
initialization of cachedAugmentations. While this ensures we do
not do the same work twice, it is a bit costly for the typical
case when the augmentations field is accessed once.

During the first call, we perform:
- a volatile read
- a lock acquire
- a volatile read
- compute the value (exclusive)
- a volatile write
- a lock release

Rather than doing that, allow the value to be computed concurrently
and use compare-and-swap to initialize it. Hence for the first call
we perform:
- a volatile read
- compute the value (concurrent)
- a compare-and-set

In case of concurrent initialization, all threads will compute
the value, but all except the first one will issue another volatile
read and throw their work away.

JIRA: MDSAL-377
Change-Id: I1dbf9c4e60cf9800720eea31bd9de936b1dae5aa
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>