torture: Make kvm.sh "Test Summary" date be end of test

Currently, the "date" command producing the output on the kvm.sh "Test
Summary" line is executed at the beginning of the test, which produces a
date that is less than helpful to someone wanting to know the duration
of the test.  This commit therefore defers this command's execution to
the end of the test.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>