index initialisation errors are ignored

[Dieterbe]

it's possible to get errors like :

cat logs/metrictank0.log | grep IDX
2016/09/20 10:49:48 [I] IDX-C Initializing. Hosts=cassandra:9042
2016/09/20 10:49:49 [cassandra.go:106 Init()] [E] IDX-C failed to initialize cassandra table. gocql: no response received from cassandra within timeout period

metrictank will run happily but not actually save any data to the index, because we ignore Init errors :
https://github.com/raintank/metrictank/blob/master/metrictank.go#L323-L343