Maps are empty if user is using phantom as browsertype

[bhavyarm]

Kibana version: 6.6.0 BC2

Elasticsearch version: 6.6.0 BC2

Server OS version: darwin_x86_64

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: If user sets the browser type to phantom in kibana.yml -
xpack.reporting.capture.browser.type: phantom , Kibana is not printing maps while doing reports.

On tilemaps - we just see data points. On region maps - just an empty page

region_map.pdf
report_phantom.pdf

[elasticmachine]

Pinging @elastic/kibana-gis

[kindsun]

This could be related to #28281 which we have a PR out for pending review. Hard to know as phantom isn't covered by caniuse (Fyrd/caniuse#2106)

[bhavyarm]

Fixed on BC3 of 6.6.0