Refactor remote transcoding tests in orch_test.go to remove time.sleep

[eliteprox]

Is your feature request related to a problem? Please describe.
Remote transcoding tests might be flaky due to a time.sleep required with go-routines to connect remote T for testing.
There are currently 5 such tests:

go-livepeer/core/orch_test.go

Line 33 in f07d69d

func TestServeTranscoder(t *testing.T) {

go-livepeer/core/orch_test.go

Line 186 in f07d69d

func TestManageTranscoders(t *testing.T) {

go-livepeer/core/orch_test.go

Line 243 in f07d69d

func TestSelectTranscoder(t *testing.T) {

go-livepeer/core/orch_test.go

Line 346 in f07d69d

func TestCompleteStreamSession(t *testing.T) {

go-livepeer/core/orch_test.go

Line 422 in f07d69d

func TestTranscoderManagerTranscoding(t *testing.T) {

Describe the solution you'd like
Refactor remote transcoding tests inside of orch_test.go to allow for remote transcoders to be connected without using go-routines or time.sleep. As recommended in #2747. One additional test should be added once resolved. I've published this to my branch here: https://github.com/eliteprox/go-livepeer/tree/develop-trancoderdrop-tests

Describe alternatives you've considered
Considered leaving the time.sleep in the tests, decision made to not add the new test at this time.

Additional context
None