New telemetry banner is not screenreader accessible

[bhavyarm]

Kibana version: 6.3.0

Elasticsearch version: 6.3.0

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 downloads

Describe the bug: New telemetry banner has auto-focus on action buttons and not screenreader accessible. Only yes or no or readmore are getting announced. Also once the option is selected - the output of that action is silent and not getting announced.

Steps to reproduce:

1. Install kibana/elasticsearch and ensure telemetry banner is getting displayed
2. Use voiceover and try to access the banner
3. Only read-more, yes or no are getting announced
4. Once you choose an option - the banner goes away silently without any announcement about whats going to happen.

Expected behavior: Telemetry banner needs to announce whats happening and the resulting action after we click it.

Related to this: #12086
Screenshots (if relevant):

[bhavyarm]

@aphelionz can you please review this?