Error response from consul kv get should be written to stderr not stdout

[pheitman]

If you have a question, please direct it to the
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addressed in either the FAQ or in one
of the Consul Guides.

When filing a bug, please include the following:

consul version for both Client and Server

Client: Consul v0.7.1
Server: Consul v0.7.1

consul info for both Client and Server

Client:

[Client `consul info` here]

Server:

agent:
	check_monitors = 0
	check_ttls = 1
	checks = 3
	services = 10
build:
	prerelease = 
	revision = 'a9455cd
	version = 0.7.1
consul:
	bootstrap = false
	known_datacenters = 1
	leader = false
	leader_addr = 192.168.2.35:8300
	server = true
raft:
	applied_index = 12488
	commit_index = 12488
	fsm_pending = 0
	last_contact = 38.772958ms
	last_log_index = 12488
	last_log_term = 2
	last_snapshot_index = 8218
	last_snapshot_term = 2
	latest_configuration = [{Suffrage:Voter ID:192.168.2.35:8300 Address:192.168.2.35:8300} {Suffrage:Voter ID:192.168.2.34:8300 Address:192.168.2.34:8300} {Suffrage:Voter ID:192.168.2.33:8300 Address:192.168.2.33:8300}]
	latest_configuration_index = 1
	num_peers = 2
	protocol_version = 1
	protocol_version_max = 3
	protocol_version_min = 0
	snapshot_version_max = 1
	snapshot_version_min = 0
	state = Follower
	term = 2
runtime:
	arch = amd64
	cpu_count = 2
	goroutines = 73
	max_procs = 2
	os = linux
	version = go1.7.3
serf_lan:
	encrypted = true
	event_queue = 0
	event_time = 14
	failed = 0
	health_score = 0
	intent_queue = 0
	left = 0
	member_time = 9
	members = 5
	query_queue = 0
	query_time = 1
serf_wan:
	encrypted = true
	event_queue = 0
	event_time = 1
	failed = 0
	health_score = 0
	intent_queue = 0
	left = 0
	member_time = 1
	members = 1
	query_queue = 0
	query_time = 1

Operating system and Environment details

CentOS 6.8

Description of the Issue (and unexpected/desired result)

consul kv get foo

returns

Error! No key exists at: foo

but it writes it to stdout and not stderr the way 'vault read secret/foo' does

Reproduction steps

Run 'consul kv get foo >/tmp/consul.out' and examine the contents of /tmp/consul.out

Log Fragments or Link to gist

Include appropriate Client or Server log fragments. If the log is longer
than a few dozen lines, please include the URL to the
gist.

TIP: Use -log-level=TRACE on the client and server to capture the maximum log detail.

[slackpad]

Fixed in #2548.