apacheGH-281: Follow first-match semantics specified for ssh config file

OpenSSH applies _all_ values from _all_ matching entries in an SSH
config file. For most keys, the first setting encountered is taken and
later values are ignored. Some keys, such as IdentityFile, behave
differently and build up a list instead.

Previously, the code tried to figure out a "best match", and applied
only the values from that entry. The new behavior is compatible with
OpenSSH.

Move the findMatchingEntries() methods from HostPatternsHolder to
HostConfigEntry, where they make more sense. Add tests for the new
behavior, and adapt some existing tests.

Bug: apache#281