Fix scenarios where error messages aren't propagated correctly (#424)

[hspedro]

Porting the routing fix that @felippeduran provided to main/v3. See #424

• Improve tests for agent and service/remote to expose bad behaviors
• Breakdown test into multiple ones to make them more clear
• Fix scenarios where error messages aren't propagated correctly

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[coveralls]

Pull Request Test Coverage Report for Build 12353837806

Details

• 17 of 36 (47.22%) changed or added relevant lines in 4 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.09%) to 59.299%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/util/util.go	0	3	0.0%
pkg/groups/etcd_group_service.go	0	4	0.0%
pkg/groups/memory_group_service.go	15	27	55.56%

Files with Coverage Reduction	New Missed Lines	%
pkg/util/util.go	1	62.0%

Totals
Change from base Build 10368957457:	0.09%
Covered Lines:	4923
Relevant Lines:	8302

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💛 - Coveralls

[felipejfc]

Will GetErrorFromPayload keep working if the server is using json serializer?

[hspedro]

Yes. The difference between unmarshalling to e.Error struct and protos.Error is a few internal XXX fields:

// Error is an error with a code, message and metadata
type Error struct {
	Code     string
	Message  string
	Metadata map[string]string
}

type Error struct {
	Code                 string            `protobuf:"bytes,1,opt,name=code" json:"code,omitempty"`
	Msg                  string            `protobuf:"bytes,2,opt,name=msg" json:"msg,omitempty"`
	Metadata             map[string]string `protobuf:"bytes,3,rep,name=metadata" json:"metadata,omitempty" protobuf_key:"bytes,1,opt,name=key" protobuf_val:"bytes,2,opt,name=value"`
	XXX_NoUnkeyedLiteral struct{}          `json:"-"`
	XXX_unrecognized     []byte            `json:"-"`
	XXX_sizecache        int32             `json:"-"`
}

So JSON serializer should still be able to serialize to protos.Error struct, just the XXX fields will be empty

[felipejfc]

only one question. apart from it, LGTM