Increase gabbi API test retry time

Currently stack API test will only retry 5 times (including the
first try) with 1 sec. interval. This might not be enough, consider
testing on some slow environment (and sometimes stack actions might
take more time). This patch increase it to 10 retries to reduce the
chances of misjudge.

Change-Id: Iea6ba608b3027965a34a5e47d3e1016c2de880f0
3 files changed