Bump gRPC dependency to v1.29.x

[jpkrohling]

Describe the bug
The current version of the gRPC client used has a behavior where it won't update the list of hosts if the initial list is empty. See jaegertracing/jaeger-operator#1175, which is likely caused by grpc/grpc-go#3353. Bumping the gRPC dependency to the latest (v1.31.1) makes it work.

To Reproduce
Steps to reproduce the behavior:

1. Using the Jaeger Operator, deploy the example agent-as-daemonset
2. Get the logs for the daemonset: $ kubectl logs daemonsets/agent-as-daemonset-agent-daemonset -f
3. See that the list of hosts isn't updated even after a couple of minutes:

$ kubectl logs daemonsets/agent-as-daemonset-agent-daemonset  -f
2020/09/01 15:13:00 maxprocs: Leaving GOMAXPROCS=6: CPU quota undefined
{"level":"info","ts":1598973180.944437,"caller":"flags/service.go:116","msg":"Mounting metrics handler on admin server","route":"/metrics"}
{"level":"info","ts":1598973180.9445577,"caller":"flags/admin.go:120","msg":"Mounting health check on admin server","route":"/"}
{"level":"info","ts":1598973180.9446096,"caller":"flags/admin.go:126","msg":"Starting admin HTTP server","http-addr":":14271"}
{"level":"info","ts":1598973180.944623,"caller":"flags/admin.go:112","msg":"Admin server started","http.host-port":"[::]:14271","health-status":"unavailable"}
{"level":"info","ts":1598973180.9454503,"caller":"grpc/builder.go:66","msg":"Agent requested insecure grpc connection to collector(s)"}
{"level":"info","ts":1598973180.9454787,"caller":"grpc@v1.28.0-pre/clientconn.go:106","msg":"parsed scheme: \"dns\"","system":"grpc","grpc_log":true}
{"level":"info","ts":1598973180.9479086,"caller":"command-line-arguments/main.go:78","msg":"Starting agent"}
{"level":"info","ts":1598973180.9479551,"caller":"healthcheck/handler.go:128","msg":"Health Check state change","status":"ready"}
{"level":"info","ts":1598973180.947995,"caller":"app/agent.go:69","msg":"Starting jaeger-agent HTTP server","http-port":5778}
{"level":"info","ts":1598973180.9573705,"caller":"dns/dns_resolver.go:212","msg":"ccResolverWrapper: sending update to cc: {[] <nil> <nil>}","system":"grpc","grpc_log":true}
{"level":"info","ts":1598973180.9574049,"caller":"grpc@v1.28.0-pre/clientconn.go:948","msg":"ClientConn switching balancer to \"round_robin\"","system":"grpc","grpc_log":true}

Bumping gRPC to the latest, after 30s in this state, the list of servers is updated:

$ kubectl logs daemonsets/agent-as-daemonset-agent-daemonset  -f
2020/09/01 15:16:04 maxprocs: Leaving GOMAXPROCS=6: CPU quota undefined
{"level":"info","ts":1598973364.7745779,"caller":"flags/service.go:116","msg":"Mounting metrics handler on admin server","route":"/metrics"}
{"level":"info","ts":1598973364.7747014,"caller":"flags/admin.go:120","msg":"Mounting health check on admin server","route":"/"}
{"level":"info","ts":1598973364.774737,"caller":"flags/admin.go:126","msg":"Starting admin HTTP server","http-addr":":14271"}
{"level":"info","ts":1598973364.7747464,"caller":"flags/admin.go:112","msg":"Admin server started","http.host-port":"[::]:14271","health-status":"unavailable"}
{"level":"info","ts":1598973364.7751777,"caller":"grpc/builder.go:66","msg":"Agent requested insecure grpc connection to collector(s)"}
{"level":"info","ts":1598973364.7751987,"caller":"grpc@v1.27.1/clientconn.go:106","msg":"parsed scheme: \"dns\"","system":"grpc","grpc_log":true}
{"level":"info","ts":1598973364.776601,"caller":"command-line-arguments/main.go:78","msg":"Starting agent"}
{"level":"info","ts":1598973364.776632,"caller":"healthcheck/handler.go:128","msg":"Health Check state change","status":"ready"}
{"level":"info","ts":1598973364.7766716,"caller":"app/agent.go:69","msg":"Starting jaeger-agent HTTP server","http-port":5778}
{"level":"info","ts":1598973364.7881553,"caller":"dns/dns_resolver.go:212","msg":"ccResolverWrapper: sending update to cc: {[] <nil> <nil>}","system":"grpc","grpc_log":true}
{"level":"info","ts":1598973364.7881958,"caller":"grpc@v1.27.1/clientconn.go:948","msg":"ClientConn switching balancer to \"round_robin\"","system":"grpc","grpc_log":true}
{"level":"info","ts":1598973394.8044846,"caller":"dns/dns_resolver.go:212","msg":"ccResolverWrapper: sending update to cc: {[{10.244.0.14:14250  <nil> 0 <nil>}] <nil> <nil>}","system":"grpc","grpc_log":true}
{"level":"info","ts":1598973394.8048198,"caller":"base/balancer.go:196","msg":"roundrobinPicker: newPicker called with info: {map[]}","system":"grpc","grpc_log":true}
{"level":"info","ts":1598973394.8062818,"caller":"base/balancer.go:196","msg":"roundrobinPicker: newPicker called with info: {map[0xc0004121c0:{{10.244.0.14:14250  <nil> 0 <nil>}}]}","system":"grpc","grpc_log":true}

Expected behavior
The gRPC client should be able to get DNS updates, especially if the initial list is empty.

Version (please complete the following information):

• Jaeger version: master as of now, v1.19.2
• Deployment: Kubernetes