[GENERIC][CASSANDRA] Loosen probe check time

With Azure and also some internal deployments, `nodepool status` takes
more than 3 seconds (it can go up to 6 seconds) and so cassandra is not
coming up or quite randomly.
This patch gives more room to `nodepool status` to answer.

Issue-ID: OOM-2687
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>
Change-Id: I98b0adc751e3cd4fa8710f88567cd8896db548eb
1 file changed