Improves methods around JavaSoftwareProcessSshDriver.installJava

Makes it much easier for subclasses to alter its behaviour, e.g. to
specify that Java 7 must be installed.
Merges JavaSPSDriverTest with JSPSDIntegrationTest

And marks testGetJavaVersion as an integration test
Merge pull request #1193 from sjcorbett/java-version-install-check

Improves methods around JavaSoftwareProcessSshDriver.installJava