tools: Run QUnit tests via test-server

Run all the QUnit tests via test-servar and http:// rather than
file:// paths.

This allows us to use actual channels and WebSocket from our
tests, rather than mocking everything out all the time.

Closes #889
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
common: Move our fdwalk() implementation to cockpitunixfd.c

And wrap it in a cockpit_unix_fd_close_all() function, since
that's what we'll use it for.

Yes, another implementation exists in session.c, but that's a
separate setuid clean-room glibc-only tool, so leave it there.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
agent: Make session dbus-daemon print address to custom fd

It seems like other output may be getting mixed in with
stdout, leading to 'Address is empty' errors.

Closes #901
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
common: Log stderr output from spawned commands to journal

This lets us assign it to the right process name in the journal
rather than letting it fall through to stderr on its own.

This also fixes logging stderr of remote cockpit-agent invocations
(ie: via ssh)

Closes #903
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
test: Add systemd scriptlets to our test spec file

Closes #904
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
static: Use PNG's instead of SVGs for branding

This helps with rendering issues on older/unstable browsers
In addition the pngs are smaller.

Fixes #908
Closes #912
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>