perf tests lock_contention: Fix shellscript errors

perf tests lock_contention: Fix shellscript errors

Use quotes around variables to prevent POSIX word expansion, use
uppercase for signals(INT, TERM, EXIT) to avoid mixed/lower case naming
of signals and replace "==" with "=" as "==" is not supported by POSIX
shell.

Signed-off-by: Abhirup Deb <abhirupdeb@linux.vnet.ibm.com>
Cc: Disha Goel <disgoel@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230613164145.50488-12-atrajeev@linux.vnet.ibm.com
Signed-off-by: Anushree Mathur <anushree.mathur2@ibm.com>
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>