JCLOUDS-549: Fix NPE in LoginCredentials.toString

- also deprecates LoginCredentails.get(Password|PrivateKey)
- use getOptionalPassword and getOptionalPrivateKey instead
JCLOUDS-622: add Strings2.toString(InputSupplier)

We did not deprecate this in 1.7.x as previously thought.
Address Checkstyle violations
Close streams in integration tests

Also remove bogus delete workaround.  Previously unclosed
FileInputStream caused test failures on Windows which cannot delete
open files.  Found with Kohsuke's file-leak-detector.
Enable more filesystem integration tests

Other tests will require Java 7 xattr support.