Fix test failure due to wait timeout

Fix test failure due to wait timeout

THe Avro and Java context integration tests waited for one second for APEX
to produce the output event to file before stopping APEX. This timeout is
usually fine. However, occasionally in the ONAP Jenkins build jobs, the
test ocassionally times out.

The tests are amended to wait for the file to exist and have content or for 10
seconds, whichever comes sooner.

Also consolidated two test classes into a single class and improved
temporary file handling.

Issue-ID: POLICY-905
Change-Id: I5e370353d2b627203e270cb6efeb560af7dc2acf
Signed-off-by: liamfallon <liam.fallon@ericsson.com>