Do most %-token substitutions in OpenSshConfig

Do most %-token substitutions in OpenSshConfig

Except for %p and %r and partially %C, we can do token substitutions
as defined by OpenSSH inside the config file parser. %p and %r can
be replaced only if specified in the config; if not, it would be the
caller's responsibility to replace them with values obtained from the
URI to connect to.

Jsch doesn't know about token substitutions at all. By doing the
replacements as good as we can in the config file parser, we can
make Jsch support most of these tokens.

%i is not handled at all as Java has no concept of a "user ID".

Includes unit tests.

Bug: 496170
Change-Id: If9d324090707de5d50c740b0d4455aefa8db46ee
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>