Improve TLS error reporting

[pingles]

We often get issues created that relate to gRPC TLS problems that aren't immediately obvious from the reported error.

For example, in #111:

{"level":"warning","msg":"error finding role for pod: rpc error: code = Unavailable desc = there is no address available","pod.ip":"172.22.6.16","time":"2018-07-04T17:11:03Z"}

Currently the only way to view these errors is by setting some gRPC environment variables:

GRPC_GO_LOG_SEVERITY_LEVEL=info
GRPC_GO_LOG_VERBOSITY_LEVEL=8

This increases the output verbosity making it easier to see the problem:

WARNING: 2017/12/21 14:53:59 grpc: addrConn.resetTransport failed to create client transport: connection error: desc = "transport: Error while dialing dial tcp [::1]:443: connect: cannot assign requested address"; Reconnecting to {[::1]:443 0  <nil>}
INFO: 2017/12/21 14:53:59 balancerWrapper: handle subconn state change: 0xc4202ea4e0, TRANSIENT_FAILURE
INFO: 2017/12/21 14:53:59 ccBalancerWrapper: updating state and picker called by balancer: CONNECTING, 0xc42023e2a0
WARNING: 2017/12/21 14:53:59 Failed to dial 127.0.0.1:443: connection error: desc = "transport: authentication handshake failed: x509: certificate is valid for localhost, kiam-server, not localhost:443"; please retry.
INFO: 2017/12/21 14:53:59 balancerWrapper: handle subconn state change: 0xc4202ea490, SHUTDOWN
INFO: 2017/12/21 14:53:59 ccBalancerWrapper: updating state and picker called by balancer: TRANSIENT_FAILURE, 0xc42023e2a0
WARN[0000] error checking health: rpc error: code = Unavailable desc = there is no connection available

It'd be nice if there was a way we could improve and report more specific errors from within the client without needing users to set environment variables.

[babatundebusari]

@pingles did you get kiam to work for you? i have this issue #164 opened but not sure if everyone else got this to work as logging is close to useless because not useful logs