Bug 11701: Fix C4::Context::Zconn

Bug 11701: Fix C4::Context::Zconn

When calling C4::Context::Zconn twice with different parameters,
the same ZOOM::Connection object is returned twice (parameters
of 2nd call are not used) This patch fixes that.

This is in part because the connection cache is keyed on server
name only. This patch corrects this by keying on all parameters.

TEST PLAN
---------
1) apply patch
2) run koha qa test tools
3) prove -v t/Context.t

The unit tests properly triggers the modified routine for
testing. Additionally, in hunting for ways it could break,
no nested synchronous or asynchronous Zconn's were found.
And even if they were, the keying on all parameters should allow
it to function properly without messing up the other connection.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>