Updated Database Entities

### PostgreSql
- Allow configuration file templates
- Set log file location as attribute
- Better control of commands used in driver
- Added shared memory and max connections configuration
- Sample `postgresql.conf` template supplied
- Added version configuration to `PostgreSqlNode`

### MariaDb and MySql
- Tidied up code
- Merged differences between entities to prepare for refactoring with parent abstract class

### Other entities
- Minor formatting and code consistency changes
- Extend and use `DatastoreCommon` and `DatastoreMixins` consistently
- Convert live tests to Java
- Added _Debian Wheezy_ to the list of operating systems tested

I have modified the `PostgreSqlNode` entity to be stricter about it's version requirements by adding the `SUGGESTED_VERSION` configuration key (defaulting to _9.1_) and then installing only `postgresql91-server` or whatever based on that value. There are some older operating systems (Debian 6 and Ubuntu 10 in particular) that do not have version 9.1 in their official repositories, so I disabled the tests that use those. The problem was that some tests were using version 8.x binaries and we have configuration that is only relevant for a 9.x PostgreSql install, things like the `shared_buffers` configuration option behave differently, for example.

Because _Debian Wheezy_ has been added, the `MariaDbNode` live tests fail there. See [brooklyn.log](https://gist.github.com/grkvlt/7915598) for details.