Integration tests don't run if port is being used

[karlaspuldaro]

Cypress tests should be able to run on another port when 8888 is used.
Trying to run make test-ui-debug command while lab is running would fail.

Command Line Output

npm run test:integration:debug
> elyra@1.4.0-dev test:integration:debug /Users/kspuldaro/github/elyra
> start-server-and-test start-jupyter http-get://localhost:8888?token=test cy:open

starting server using command "npm run start-jupyter"
and when url "http-get://localhost:8888?token=test" is responding
running tests using command "cy:open"

> elyra@1.4.0-dev start-jupyter /Users/kspuldaro/github/elyra
> mkdir -p build/cypress-tests && jupyter lab --config=./tests/test-config.py

[I 17:12:08.948 LabApp] The port 8888 is already in use.
[C 17:12:08.948 LabApp] ERROR: the notebook server could not be started because port 8888 is not available.
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! elyra@1.4.0-dev start-jupyter: `mkdir -p build/cypress-tests && jupyter lab --config=./tests/test-config.py`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the elyra@1.4.0-dev start-jupyter script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/kspuldaro/.npm/_logs/2020-10-27T21_12_09_022Z-debug.log
Error: server closed unexpectedly
    at ChildProcess.onClose (/Users/kspuldaro/github/elyra/node_modules/start-server-and-test/src/index.js:60:14)
    at ChildProcess.emit (events.js:321:20)
    at maybeClose (internal/child_process.js:1026:16)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:286:5)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! elyra@1.4.0-dev test:integration:debug: `start-server-and-test start-jupyter http-get://localhost:8888?token=test cy:open`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the elyra@1.4.0-dev test:integration:debug script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/kspuldaro/.npm/_logs/2020-10-27T21_12_09_097Z-debug.log
make: *** [test-ui-debug] Error 1