Fix usr.bin/procstat/tests to be executed in parallel mode

[olivier]

Summary

All usr.bin/procstat tests are using the same filename procstat.out, that could create conflict if executed with parallelism enabled: switching to a dedicated filename.

[asomers]

It doesn't matter, because Kyua executes the tests in separate temporary directories.

[olivier]

You've right, those are not the source of the problem.
For history, here is the problem sometimes happen in parallel mode:

usr.bin.procstat.procstat_test.kernel_stacks (from (test-report.xml))

Failing for the past 1 build (Since Unstable#3422 )
Took 0.35 sec.
add description
Error Message
atf-check failed; see the output of the test for details
Standard Output
Executing command [ procstat -a kstack ]
Standard Error
Test case metadata
------------------

allowed_architectures is empty
allowed_platforms is empty
description = Captures kernel stacks for all visible threads
has_cleanup = false
is_exclusive = false
required_configs is empty
required_disk_space = 0
required_files is empty
required_memory = 0
required_programs is empty
required_user is empty
timeout = 300

Timing information
------------------

Start time: 2021-03-16T21:20:31.257142Z
End time:   2021-03-16T21:20:31.608909Z
Duration:   0.352s

Original stderr
---------------

Fail: stderr not empty
--- /dev/null	2021-03-16 21:20:31.519139000 +0000
+++ /tmp/kyua.T7vVVo/3134/work/check.tL25KQ/stderr	2021-03-16 21:20:31.516474000 +0000
@@ -0,0 +1 @@
+procstat: sysctl: kern.proc.pid: 19263: No such process

[arichardson]

In D29290#656428, @olivier wrote:

You've right, those are not the source of the problem.
For history, here is the problem sometimes happen in parallel mode:

usr.bin.procstat.procstat_test.kernel_stacks (from (test-report.xml))

Failing for the past 1 build (Since Unstable#3422 )
Took 0.35 sec.
add description
Error Message
atf-check failed; see the output of the test for details
Standard Output
Executing command [ procstat -a kstack ]
Standard Error
Test case metadata
------------------

allowed_architectures is empty
allowed_platforms is empty
description = Captures kernel stacks for all visible threads
has_cleanup = false
is_exclusive = false
required_configs is empty
required_disk_space = 0
required_files is empty
required_memory = 0
required_programs is empty
required_user is empty
timeout = 300

Timing information
------------------

Start time: 2021-03-16T21:20:31.257142Z
End time:   2021-03-16T21:20:31.608909Z
Duration:   0.352s

Original stderr
---------------

Fail: stderr not empty
--- /dev/null	2021-03-16 21:20:31.519139000 +0000
+++ /tmp/kyua.T7vVVo/3134/work/check.tL25KQ/stderr	2021-03-16 21:20:31.516474000 +0000
@@ -0,0 +1 @@
+procstat: sysctl: kern.proc.pid: 19263: No such process

That sounds like procstat -a should handle processes dying better.