bridge: When expanding package variables, use package names

Use the real package names when expanding package variables, if
not using checksums.

Closes #1401
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
common: Allow telling pipe not to touch stderr

This should be used in test-server, so that people debugging can
see cockpit-bridge output on the real terminal stderr.
bridge: Ignore possibly fatal warnings when installing polkit agent

This is a workaround for a polkit bug, which emits a pretty strong
g_warning() when it can't install a polkit agent. We ignore this
warning, but also ignore the possibly fatal debugging abort()
here.
common: Include new lines in stderr output when forwarding

When forwarding stderr output to the logs, include new lines so
that the when the messages are also relayed to stderr they look
correct.
ws: test-server now runs cockpit-bridge with fatal warnings/criticals

This allows us to debug problems, run under valgrind, etc.
Run test-server under valgrind as well as other test child processes
tools: Add polkit.supp for suppressing polkit leaks

HACK: https://bugs.freedesktop.org/show_bug.cgi?id=85506
common: Simpler removing of signal handlers in CockpitPipeTransport
ws: Use 'cat' as a mock bridge in certain tests

This is simpler, faster, and makes a lot less journal and valgrind
noise.
tools: Ignore more supurious leaks