tools/rcutorture: Make identify_qemu_vcpus() independent of local language

The rcutorture scripts' identify_qemu_vcpus() function expects `lscpu`
to have a "CPU: " line, for example:

	CPU(s):		8

But different local language settings can give different results:

	Processeur(s) :		8

As a result, identify_qemu_vcpus() may return an empty string, resulting
in the following warning (with the same local language settings):

	kvm-test-1-run.sh: ligne 138 : test:  : nombre entier attendu comme expression

This commit therefore changes identify_qemu_vcpus() to use getconf,
which produces local-language-independend output.

Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: rcu@vger.kernel.org
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>