docs(samples): updated samples code to use async await

[praveenqlogic]

Fixes googleapis/google-cloud-node#2869 (it's a good idea to open an issue first for discussion)
Fixes https://github.com/googleapis/nodejs-video-intelligence

• Tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

[codecov]

Codecov Report

Merging #151 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #151   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines           8      8           
=====================================
  Hits            8      8

---

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 282dc4d...0248dc2. Read the comment docs.