Define default OS_TEST_TIMEOUT for every tempest tox env

Currently only 'all' tox env define the default OS_TEST_TIMEOUT
which is 1200. Any other tox env which run tempest test does not
have any default value for test timeout.

We should define default OS_TEST_TIMEOUT in every such env like
'all'.

Change-Id: I0dc4c940bbb22321b42e0f242aea5c1b5f45a5ae
1 file changed