Increase default maxRetainedLogMessages

With only 10 lines, CF Acceptance Tests fails on a default v172
installation, because the expected Cloud Controller message rolls off.
We're requesting 100 lines, because the staging environments use this
setting.

Signed-off-by: Ryan Tang <ryantang@pivotallabs.com>
Merge pull request #410 from cloudfoundry/update-loggregator-spec

Increase default maxRetainedLogMessages