Fix issue with ti-stress not requesting correct capabilities

The tistress agent was failing to request the
can_get_source_debug_extension capability causing it to fail to get
all the information it should have been retrieving.

Test: ./test/run-test --host \
                      --dev \
                      --jvmti-redefine-stress \
                      --jvmti-trace-stress 001-HelloWorld

Change-Id: I234a08f382ba0284ab9e3d441056b0221c7df262