Reduce minimum delay when running on ppc64el

Hello,

We have noticed some failures during autopkgtest on Ubuntu/ppc64el due to the delay test:

http://autopkgtest.ubuntu.com/packages/fence-agents/hirsute/ppc64el https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-hirsute/hirsute/ppc64el/f/fence-agents/20210226_210546_29714@/log.gz

The reason, as far as I have investigated, is because the delay on ppc64el can be lower than 1000ms. After analysing some of the failing tests' logs, I was able to determine that the delay is always lower than 1000ms, but greater than 500ms. Therefore, I would like to proposed this change to the package. It is conservative in the sense that the minimum delay is adjusted only when running on ppc64el, but I'd appreciate your review especially because I could not figure out where the value of 1000 came from.

Thanks.