torture: Create kvm-check-branches.sh output in proper location

Currently, kvm-check-branches.sh causes each kvm.sh invocation create a
separate date-stamped directory, then after that invocation completes,
moves it into the *-group/NNNN directory. This works, but makes it more
difficult to monitor an ongoing run. This commit therefore uses the
kvm.sh --datestamp argument to make kvm.sh put the output in the right
place to start with, and also dispenses with the additional level of
datestamping. (Those wanting datestamps can find them in the log files.)

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

torture: Change KVM environment variable to RCUTORTURE

The torture-test scripting's long-standing use of KVM as the environment
variable tracking the pathname of the rcutorture directory now conflicts
with allmodconfig builds due to the virt/kvm/Makefile.kvm file's use
of this as a makefile variable. This commit therefore changes the
torture-test scripting from KVM to RCUTORTURE, avoiding the name conflict.

Reported-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Tested-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

torture: Make kvm-check-branches.sh use --allcpus

Currently the kvm-check-branches.sh script calculates the number of CPUs
and passes this to the kvm.sh --cpus command-line argument. This works,
but this commit saves a line by instead using the new kvm.sh --allcpus
command-line argument.

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

torture: Add script to smoke-test commits in a branch

This commit adds a kvm-check-branches.sh script that takes a list
of commits and commit ranges and runs a short rcutorture test on all
scenarios on each specified commit. A summary is printed at the end, and
the script returns success if all rcutorture runs completed without error.

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