Improve messaging and setup process for configuring outbound email.

Summary:

• Make the instructional text generally more useful.
  • Show the current configured adapter.
  • When the configuration prevents outbound email from being delivered, show a

warning.

• Detect 'curl' extension during setup since it's more-or-less required
• Add curl extension to the install scripts

codeblock: can you verify the rhel-derivs changes are correct?

Test Plan:
Set adapter to test, verified warning; entered setup mode and verified curl. Ran
apt-get on an ubuntu box. Ran yum on an amazon linux box.

Reviewed By: toulouse
Reviewers: toulouse, codeblock
Commenters: codeblock
CC: aran, jungejason, tuomaspelkonen, codeblock, epriestley, toulouse
Differential Revision: 438