http json output plugin

[vikrant6]

[vikrant6]

System info:

[Include Telegraf version, operating system name, and other relevant details]

telegraf version 1.7.0
mac os

Steps to reproduce:

Configure the http output plugin to post to an https endpoint.

[[inputs.cpu]]
  ## Whether to report per-cpu stats or not
  percpu = true
  ## Whether to report total system cpu stats or not
  totalcpu = true
  ## If true, collect raw CPU time metrics.
  collect_cpu_time = false
  ## If true, compute and report the sum of all non-idle CPU states.
  report_active = false


# Read metrics about memory usage
[[inputs.mem]]
    ...
    ...

Expected behavior:
post json to the configured url
Actual behavior:
Errors out and crashes with below error

anic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x38 pc=0x4dbe75a]

goroutine 8 [running]:
github.com/influxdata/telegraf/plugins/outputs/http.(*HTTP).write(0xc420446000, 0xc4200fc900, 0x5d8, 0x8d3, 0x0, 0x0)
	/private/tmp/telegraf-20180614-31387-h4ela8/telegraf-1.7.0/src/github.com/influxdata/telegraf/plugins/outputs/http/http.go:131 +0xca
github.com/influxdata/telegraf/plugins/outputs/http.(*HTTP).Write(0xc420446000, 0xc42030c1e0, 0x5, 0x5, 0xc420300101, 0xc4203dbe68)
	/private/tmp/telegraf-20180614-31387-h4ela8/telegraf-1.7.0/src/github.com/influxdata/telegraf/plugins/outputs/http/http.go:121 +0x97
github.com/influxdata/telegraf/internal/models.(*RunningOutput).write(0xc4200d8dc0, 0xc42030c1e0, 0x5, 0x5, 0x0, 0x0)
	/private/tmp/telegraf-20180614-31387-h4ela8/telegraf-1.7.0/src/github.com/influxdata/telegraf/internal/models/running_output.go:179 +0xf7
github.com/influxdata/telegraf/internal/models.(*RunningOutput).Write(0xc4200d8dc0, 0x52b42a8, 0xc420296180)
	/private/tmp/telegraf-20180614-31387-h4ela8/telegraf-1.7.0/src/github.com/influxdata/telegraf/internal/models/running_output.go:161 +0x462
github.com/influxdata/telegraf/agent.(*Agent).flush.func1(0xc420296180, 0xc4200d8dc0)
	/private/tmp/telegraf-20180614-31387-h4ela8/telegraf-1.7.0/src/github.com/influxdata/telegraf/agent/agent.go:232 +0x59
created by github.com/influxdata/telegraf/agent.(*Agent).flush
	/private/tmp/telegraf-20180614-31387-h4ela8/telegraf-1.7.0/src/github.com/influxdata/telegraf/agent/agent.go:230 +0xa3
Additional info:

[Include gist of relevant config, logs, etc.]

[glinton]

@vikrant6 I'm not sure if you were able to continue, but you'll need to ensure the url format in your output block matches the following: [scheme:][//[userinfo@]host][/]path[?query][#fragment]