[Reporting] Canvas multi-page PDF export doesn't include the entire worksheet

[tsullivan]

Kibana version: 8.0/master

1. Export the eCommerce worksheet as a PDF file. The PDF should contain 2 pages
2. The result PDF doesn't include all the pages.

The logs are showing that both pages of the worksheet are opening simultaneously with 2 different browser drivers:

Logs:

server    log   [09:38:29.059] [debug][esqueue][queue-worker][reporting] k5y3r7qq1vh57a3f11b09y1p - 1 outstanding jobs returned
server    log   [09:38:29.090] [info][esqueue][queue-worker][reporting] k5y3r7qq1vh57a3f11b09y1p - Job marked as claimed: /.reporting-2020.01.26/k5y3ukkc1vh57a3f11440joc
server    log   [09:38:29.091] [info][esqueue][queue-worker][reporting] k5y3r7qq1vh57a3f11b09y1p - Starting job
server    log   [09:38:29.150] [info][browser-driver][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Creating browser page driver
server    log   [09:38:29.169] [info][browser-driver][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Creating browser page driver
server    log   [09:38:29.737] [debug][browser-driver][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Browser page driver created
server    log   [09:38:29.742] [info][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] opening url https://localhost:443/kbn/app/canvas#/export/workpad/pdf/workpad-e08b9bdb-ec14-4339-94c4-063bddfd610e/page/1?forceNow=2020-01-28T16%3A38%3A28.762Z
server    log   [09:38:29.764] [debug][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Using custom headers for https://localhost/kbn/app/canvas
server    log   [09:38:29.819] [debug][browser-driver][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Browser page driver created
server    log   [09:38:29.821] [info][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] opening url https://localhost:443/kbn/app/canvas#/export/workpad/pdf/workpad-e08b9bdb-ec14-4339-94c4-063bddfd610e/page/2?forceNow=2020-01-28T16%3A38%3A28.762Z
server    log   [09:38:29.828] [debug][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Using custom headers for https://localhost/kbn/app/canvas
server    log   [09:38:30.308] [debug][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Using custom headers for https://localhost/kbn/bundles/app/canvas/bootstrap.js
server    log   [09:38:30.345] [debug][execute][k5y3ukkc1vh57a3f11440joc][printable_pdf][reporting] Using custom headers for https://localhost/kbn/bundles/app/canvas/bootstrap.js

[elasticmachine]

Pinging @elastic/kibana-reporting-services (Team:Reporting Services)