Index of drillbits + Zookeeper Path

[JohnCoene]

Thank you for the great package, I'm relying on it quite a bit now, I'm just encountering two issues:

1. See SetMaxOpenConns > zookeepers #5, we check for d.nextBit >= len(newClient.drillBits) but eindex can remain out of range.

go-drill/client.go

Line 155 in eb99719

eindex := d.nextBit

2. The other issue, I'm not sure why sometimes the path is wrong and set to mydrillbit instead of /drill/mydrillbit.

go-drill/zk_handler.go

Line 76 in eb99719

data, _, err := z.conn.Get(z.Path + "/" + drillbit)

This causes the connection to error ("invalid path") but it seems z.Err is never really checked. I'm not sure where this should be checked though.

go-drill/zk_handler.go

Line 78 in eb99719

z.Err = err

This PR fixes these, though maybe not elegantly.

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