Increase timeout for arithmetic testsuite

I've seen a number of timeouts on that testsuite when running
under valgrind (typically when the CI infrastructure is under
load). Increase the timeout to reduce the number of failing
jobs due to a low timeout.

Change-Id: I9563503fa05b20c35d19fb776ef10959332557b0
Reviewed-on: http://review.couchbase.org/82954
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>

Author: trondn

tests/testapp/CMakeLists.txt

@@ -96,7 +96,7 @@ add_unit_test_suite(NAME require-init
 
 # Run the Arithmetic tests
 add_unit_test_suite(NAME arithmetic
-                    TIMEOUT 120
+                    TIMEOUT 240
                     SOURCE testapp_arithmetic.cc testapp_arithmetic.h)
 
 # Run the Audit tests