Add details to 'TarantoolClientException: Failed to refresh spaces and indexes metadata' error

[vrogach2020]

Now if ddl.get_schema() returns nil we get a nested NPE. It would be nice to have a sane error here

Exception in thread "main" io.tarantool.driver.exceptions.TarantoolClientException: Failed to refresh spaces and indexes metadata
	at io.tarantool.driver.core.metadata.TarantoolMetadata.awaitInitLatch(TarantoolMetadata.java:89)
	at io.tarantool.driver.core.metadata.TarantoolMetadata.getSpaceMetadata(TarantoolMetadata.java:41)
	at io.tarantool.driver.core.metadata.TarantoolMetadata.getSpaceByName(TarantoolMetadata.java:126)
	at io.tarantool.driver.core.ProxyTarantoolClient.space(ProxyTarantoolClient.java:110)
	at ru.mail.javaexample.DataReader.read(DataReader.java:29)
	at ru.mail.javaexample.App.main(App.java:28)
Caused by: java.lang.NullPointerException
	at io.tarantool.driver.core.metadata.TarantoolMetadata.lambda$populateMetadata$2(TarantoolMetadata.java:105)
	at java.util.concurrent.CompletableFuture.uniAccept(CompletableFuture.java:670)
	at java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:646)
	at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:488)
	at java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:1975)
	at io.tarantool.driver.handlers.TarantoolResponseHandler.channelRead0(TarantoolResponseHandler.java:51)
	at io.tarantool.driver.handlers.TarantoolResponseHandler.channelRead0(TarantoolResponseHandler.java:23)
	at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:327)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:299)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:722)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:658)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:584)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:496)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:748)