Force tls1.2 on old android

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What

Added a custom SSLSocketFactory for enabling TLS1.2 on Android API < 20.

How

Android API >= 20 already has TLS1.2 enabled by default. API level 19 has it available but not enabled. On older versions of Android it is possible for users to workaround this, for example by configuring the HttpsUrlConnection.setDefaultSocketFactory or similar. However, we can check the API version and set the socket factory for each HttpConnection automatically so that older versions of Android work without any user required changes.

Added Android version and TLS support checks as well as a TLSv1.2 only SSLSocketFactory to enable on older versions.
Moved default interceptors into CouchClient from ReplicatorBuilder.

Testing

Updated HttpTest that called HttpConnection directly to consume default interceptors.
Refactored HttpTest slightly to simplify interceptor addition.
Updated replication tests for new assertions, due to interceptor move to CouchClient and interceptor "sizes".

Existing tests pass. Manually tested on API 19 emulator against TLS1.2 only Cloudant. CI tests run against API >= 20, so don't regularly check this. We could consider an extra branch of testing using the emulator at API level 19.

Issues

N/A

cloudant / sync-android