MULE-7097: Provide a way to specify valid cipher specs for SSL on transports that support the protocol

Backport of the feature that enables to configure enabled protocols and ciphers for SSL by adding the tls-default file in the conf folder. This is a cherry pick of: ea8b6af, 28a9c07 and f886a2d, with manual changes required in the Jetty transport because of the version of the library.
(cherry picked from commit 19d92e9)
MULE-6926: Fix flaky tests

Adding missing import