Enhancement: Unit tests for datasources classes - Part 1 & Fixes

Unit tests for OCLocalAppRegistryDataSource, OCRemoteAppRegistryDataSource, OCLocalAuthenticationDataSource,
OCRemoteAuthenticationDataSource, OCLocalCapabilitiesDataSource and OCRemoteCapabilitiesDataSource classes have
been done and completed, and several fixes have been applied to all existent unit test classes for
datasources.

https://github.com/owncloud/android/issues/4063
https://github.com/owncloud/android/pull/4209
