test_importRawBlock doesn't handle errors properly

[gumb0]

It succeeds even if the block import failed.

@winsvega reports that this is what happens when importing invalid block:

WARN  06-30 14:53:01 aleth warn   
                                                                                
                                                                                
    Import Failure     /home/wins/Ethereum/cpp-ethereum/libethereum/Block.cpp(565): Throw in function dev::u256 dev::eth::Block::enact(const dev::eth::VerifiedBlockRef&, const dev::eth::BlockChain&)
Dynamic exception type: boost::exception_detail::clone_impl<dev::eth::UncleInChain>
[dev::tag_comment*] = Uncle in block already mentioned
[dev::eth::tag_uncleIndex*] = 1
[dev::eth::tag_unclesExcluded*] = { 9e38ab1792276d10df19067001684545b2c905a44423f6e50b1835b12b3ac3ef, 3874ace79c930a81d6c8e77c2eaec5c2d474678c120ce35c2aa3c5bf25bf8012, 250c192ac598dcc6d79142a983be39358eeba2547d689b91cab661da74aa5cfa, 5a39ed1020c04d4d84539975b893a4e7c53eab6c2965db8bc3468093a31bc5ae, 2b6e0badc6ea187cc798918e1515dcbe3f0e1cecec42dcd51e63a63cdf2f1e66 }
[dev::eth::tag_now*] = 1561895581
[dev::eth::tag_block*] = [ type: std::vector<unsigned char, std::allocator<unsigned char> >, size: 24, dump: d0 3b 05 b8 64 7f 00 00 2c 42 05 b8 64 7f 00 00 ]
[dev::tag_hash*] = 250c192ac598dcc6d79142a983be39358eeba2547d689b91cab661da74aa5cfa
    
                                                                                
                       Bad Block #00000003.2b6e0bad…                      
                                                                                
                                                                                
TRACE 06-30 14:53:01 aleth rpc    {"id":118,"jsonrpc":"2.0","result":"0x2b6e0badc6ea187cc798918e1515dcbe3f0e1cecec42dcd51e63a63cdf2f1e66"}

aleth/libethereum/ClientTest.cpp

Lines 157 to 163 in be6ce38

	bool moreToImport = true;
	while (moreToImport)
	{
	tie(ignore, moreToImport, ignore) = syncQueue(100000);
	this_thread::sleep_for(chrono::milliseconds(100));
	}
	return blockHash;

The simple fix to try would be to look at fresh blocks returned as the first value from syncQueue. If blockHash was not returned there, it means it was rejected as bad block, and then we should throw exception in this case.