INT-3155: add Gradle task 'testAll'

* Add to `LongRunningIntegrationTest` ability to read `System.properties`
Note, ENV property 'RUN_LONG_INTEGRATION_TESTS' has a preference in case of value `true`
* Add Gradle task `testAll`
* Upgrade to Gradle 1.7
* Improve build performance by adding 'inputs'/'outputs' to some tasks

JIRA: https://jira.springsource.org/browse/INT-3155