test: Fix TestShutdownRestart.testBasic for different OS timezones
test: Fix TestShutdownRestart.testBasic for different OS timezones

This test queried the host's date to schedule a shutdown for the VM.
Our RHEL images run in the EDT time zone, so after 20:00 EDT the host
already moved to the next day, and the test would schedule the shutdown
for the wrong day. Avoid this by querying the VM's date instead.

mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit