oeqa/runtime/cases/ptest: Increase test timeout from 300s to 450s

Some tests such as lttng-tools are marginal and timing out on the autobuilder
with the current 300s default. Increase to avoid this noise in the ptest
failures list.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 5fb902a5)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>