[HTTP probe] Add capability to run multiple parallel probes per cycle

[manugarg]

HTTP probe enhancement:

Add capability to run multiple parallel probes per cycle. This is useful if someone wants to run a lot of HTTP probes against a target without increasing prober footprint.

CC: @ls692

[aidarbek]

Do I understand it correctly that we need to execute this loop concurrently (with goroutines)?

cloudprober/probes/http/http.go

Line 311 in c153aa4

for ts := range ticker.C {

Also, should it be optional (by specifying command line argument), as DNS probe runs in parallel by default?

cloudprober/probes/dns/dns.go

Line 205 in c153aa4

for _, target := range p.targets {

[manugarg]

@aidarbek Yeah, something like that. I hacked up something last night. I'll send you a CL? :)

(Sorry, should have assigned it to myself before working on it.)

[manugarg]

Marking closed. To track the release of this feature, please look at #326.