Add PDO $options support

Problem/Motivation

Db services may require additional settings to be sent to the connection string via the PDO $options parameter. See PDO::__construct.

For example, Azure DB for MySQL/MariaDB requires a cert to be attached to the PDO connection.

Steps to reproduce

• Add a new Aegir server to an Azure DB for MySQL server (with the default "Enforce SSL connection" setting)
• Observe the verify task fails with SQLSTATE[HY000] [9002] SSL connection is required. Please specify SSL options and retry.

Proposed resolution

I'd recommend a solution similar to the one that was implemented in SimpleSAMLphp. We'll need to add an options field in the UI then hook it up in Provision/Service/db/pdo.php.

Remaining tasks

• Add a (multivalued?) options field in the server definition.
• Write the options out to the PDO connection.

(I'm sure there's more)

User interface changes

API changes

Data model changes