Support Microsoft Azure SQL Database

[gossion]

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[cfdreddbot]

Hey gossion!

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[cf-gitbot]

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[gossion]

(modified from conversation of cloudfoundry/bbs#17)
Hi,

I submit this PR in the purpose of supporting MSSQL (Microsoft / Azure SQL Server) for CF Diego.
Currently mysql and postgres are supported in Diego, in this PR I am trying to make mssql (especial for Azure PAAS - Azure SQL server) as another option for Diego databases.

There are 3 PRs to support this feature:

1. On bbs: Support Microsoft SQL server on diego bbs bbs#17 - Logic to make mssql available for bbs.
2. On locket: Support Microsoft SQL server (mssql) locket#2 - The change is mostly for making diego unit test pass, though I don't see how to use locket in a CF deployment.
3. On diego-bbs: Support Microsoft Azure SQL Database #278 - Change job spec and package to support mssql. (this PR)

Unit test and CF acceptance test were run for these 3 PRs, no issue found. Tests were done against diego v1.7.1 and CF v252

Notes: (If you are okay to do the merge, or if you want to rework these PRs)

1. PR#1,2 need to be merged before PR#3.

2. You need to prepare a SQL Server environment to make diego unit test passed when PR#3 is merged. there are two options to prepare the environment:

   A. Test against local SQL server: Setup a SQL server in localhost according to this guide(Guide has also been updated to diego-release/CONTRIBUTING.md). And export a SQL ConnectionString before launching the test, like this:

       export MSSQL_BASE_CONNECTION_STRING="server=localhost;user id=diego;password=Password-123;port=1433"; ./scripts/run-unit-tests     #this connection string should not contain 'database=..' because database will be created automatically when running unit test.
   

   B. Test against an Azure SQL server: You need to create a SQL server on Azure, set the firewall to allow connection from your test IP. And export a SQL ConnectionString before launching the test, like this:

       export MSSQL_BASE_CONNECTION_STRING="server={your_dbserver_name};user id={your_username};password={your_password};port=1433"; ./scripts/run-unit-tests     #this connection string should not contain 'database=..' because database will be created automatically when running unit test.
   

3. To use on-premise SQL server in CF deployment Diego BBS, you can configure it on properties.diego.bbs.sql on your CF manifest, for example:

   sql:
     ca_cert: null
     db_connection_string: null
     db_driver: mssql
     db_host: {your_dbserver_name}
     db_password: {your_password}
     db_port: 1433
     db_schema: {your_dbname}
     db_username: {your_username}
     max_open_connections: null
     require_ssl: null
   

[emalm]

As per cloudfoundry/bbs#17 (comment), closing as stale.

Best,
Eric, CF Diego PM