Add ability to runStorage with specific identifier

[cblp]

for cases when we cannot guarantee a unique MAC.

And a random id when we even cannot specify one.

[iupii]

How we should specify one? By new argument to newHandle? Something like:

newHandle :: FilePath -> Maybe Word64 -> IO Handle
newHandle hDataDir hReplicaId = do
...
hReplica <- applicationSpecific <$> fromMaybe getRandomId (getMacAddress <|> hReplicaId)
...

[cblp]

@iupii, yes, good idea.

But it would be better to have a separate function, say, newHandleWithReplica

[cblp]

And there shouldn't be random id in presence of explicit id.

[iupii]

With explicit id

newHandleWithReplicaId :: FilePath -> Maybe Word64 -> IO Handle
newHandleWithReplicaId hDataDir hReplicaId = do

Without

newHandle :: FilePath -> IO Handle
newHandle hDataDir = do
...
hReplica <- applicationSpecific <$> fromMaybe getRandomId getMacAddress

[cblp]

Yes, go for it!

[iupii]

Which random library fits?

[iupii]

With tf-random https://github.com/iupii/ron/commit/1c467faf5878d367ae66f5e3832f4d660f78f119

[cblp]

PR please

[cblp]

Cool, but rewrite (=<<), (<*>) and nested (<$>) with do-notation to lower barrier.

[cblp]

done in #107