perf testsuite: Add common setting for shell tests

Add settings defining sample commands later shared by shell tests. This
adds the possibility to globally adjust the default values for the whole
testsuite.

Signed-off-by: Veronika Molnarova <vmolnaro@redhat.com>
Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Cc: kjain@linux.ibm.com
Cc: atrajeev@linux.vnet.ibm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240215110231.15385-3-mpetlan@redhat.com