Fix result cache and PDO connection test on pdo_sqlsrv

Fix closing statement cursor on pdo_sqlsrv if not executed yet

[DBAL-2637] Fix closing prepared statement cursor with LOB column on Oracle

Fix dropping inuse databases on SQL Server and Oracle

Fix the reuse of a statement on sqlsrv with explicit bindValue()

Tear down active transactions in functional test cases

Fix drivers' exec() method to not execute via prepared statements

[DBAL-2623] Fix Generic SQL Sharding Support documentation example

HHVM testing needs to be in PHP 7 mode

Fix fetching last insert ID for sequences on SQL Server

Fix date diff test

Fix CREATE/DROP DATABASE support on SQL Server

[DBAL2626] Add PHPUnit config for continuousphp Oracle testing

Fix "application_name" test on PostgreSQL < 9.2

Run SQL Azure related tests conditionally

[DBAL-2427] Fix negative default value introspection on PostgreSQL 9.4

Prepared statements become unusable after calling closeCursor() on IBM DB2, Oracle and MS SQL Server.

- Suspend HHVM testing until the following items are resolved
  - HHVM PHP 7 mode issues.
    - facebook/hhvm#7626 php 7 mode not recognized by composer as PHP 7
    - facebook/hhvm#7198 type annotations on internal functions, `expects parameter 1 to be _______, null given`
    - facebook/hhvm#7544 HHVM INI settings for PHP7 mode `php 7 is not the same as php 7.1`
  - Trusty Container issues (currently beta)
    - https://github.com/travis-ci/travis-ci/issues/6842 - MySQL socket issue on Trusty beta Container (assume fixed sometime after 1Q17)
- Add line to Force hhvm PHP 7 mode for future testing
  - HHVM fails on composer `This package requires php ^7.0 but your HHVM version does not satisfy that requirement`
  - reference for change https://docs.hhvm.com/hhvm/configuration/INI-settings#php-7-settings

[DBAL-2546] Fixed the failure of `Functional\StatementTest::testReuseStatementWithParameterBoundByReference()` on ibm_db2

The test is partially skipped due to:

1. Fetching blob as binary string from pdo_sqlsrv requires using `PDOStatement::bindColumn()` and `PDOStatement::fetch(PDO::FETCH_BIND)` which are not supported by the DBAL.
2. Setting encoding on the connection level is not supported: https://msdn.microsoft.com/en-us/library/ff628164(v=sql.105).aspx

[DBAL-2546] Fixed the failure of `Functional\StatementTest::testIncompletelyFetchedStatementDoesNotBlockConnection()` on pdo_mysql + libmysql

The test case being fixed should reset shared connection during teardown as one if its methods modifies connection attributes.