[build/fs] Fix copyAll default atime and mtime

[jbudz]

When copying files during builds we're passing a default of Date.now() (time since epoch in ms) to fs.utimes. fs.utimes expects this argument to be in seconds. This can result in a corrupt timestamp on file access and file modified:

~/Downloads/tmp » tar -xvf kibana-7.11.0-docker-build-context.tar.gz                                                                                                             
Dockerfile                                                                                                                                                                                                         
bin/                                                                                                                                                                                                               
config/                                                                                                                                                                                                            
tar: Archive contains ‘0-250645035 ’ where numeric time_t value expected                                                                                                                                           
bin/kibana-docker                                                                                                                                                                                                  
tar: bin/kibana-docker: implausibly old time stamp 1969-12-31 17:59:59                                                                                                                                             
tar: Archive contains ‘0-250645031 ’ where numeric time_t value expected                                                                                                                                           
config/kibana.yml                                                                                                                                                                                                  
tar: config/kibana.yml: implausibly old time stamp 1969-12-31 17:59:59                                                                                                                                             
tar: Exiting with failure status due to previous errors  

Behavior appears to be inconsistent across build environments. Locally, I'm setting the year to 2446, in contrast to the 7.11.0 BC above with a year of 1969.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 147ab87

Metrics [docs]

✅ unchanged

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[spalger]

LGTM

[jbudz]

7.x: d8ef1b4
7.11: 2d86004
7.10: e433cbf