Add support for MySQL/MariaDB and Postgres + fixes

[setrofim]

Add support for "mysql" and "pgx" drivers (for MySQL/MariaDB and Postgres, respectively). This required the following changes to the "sql" kvstore backend:

• "key" column had to be renamed to "kv_key", as the former is a reserved word in MySQL. "vals" column has also been renamed to "kv_val" for consistency (also, the old name implied that the column contained an array of values, where as it is a single string value).
• Queries are now assembled using squirrel, which allows switching the placeholder symbol. This is necessary because MySQL and Postgres expect different syntax for placeholders.

Documentation for KVStore has been amended to reflect that only three drivers can be enabled via configuration for the services, and the described support for other drivers is in the context of other code using the KVStore implementation. (Plus minor line length re-formatting.)

Native deployment has been augmented with optional config/init scripts for the other SQL drivers, and documentation on how to enable them.

Additionally:

• Update end-to-end input corims to the new format
• Allow -f and -s flags at the same time when creating a native deployment

[yogeshbdeshpande]

I do not have additional comments, I looked at the code and I had same questions as asked by Thomas so once you address them, I am fine with the change!