wdio-selenium-standalone: fix watch mode

[fastmx]

Selenium was exiting after first run. This triggered an error on next attempts.

Proposed changes

Add/fix support for watch mode #3897

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

I'm not sure if there is other way to listen on process exit (so i did it on top level). If you have any suggestion to this bit then i'm open 👍

Reviewers: @webdriverio/technical-committee

[fastmx]

@christian-bromann CLA is signed; new pr because previous changes vanished after force push in wrong time

[codecov]

Codecov Report

Merging #3970 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3970      +/-   ##
==========================================
+ Coverage   98.59%   98.59%   +<.01%     
==========================================
  Files         154      154              
  Lines        3477     3487      +10     
  Branches      763      765       +2     
==========================================
+ Hits         3428     3438      +10     
  Misses         44       44              
  Partials        5        5

Impacted Files	Coverage Δ
...s/wdio-selenium-standalone-service/src/launcher.js	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8f1025c...110b307. Read the comment docs.

[christian-bromann]

👍 thanks!