[JENKINS-22820] fix - Bump maven.scm to 1.9.1 to avoid issues with Git v1.9 upgrades.

Upgrade to latest Jenkins to do testing.

Specify plexus-maven-plugin version.

Bump maven-scm-provider-svnjava to later version.

The v1.9.1 version changes to use --porcelain mode, which prevents the parsing bug.

![image](https://cloud.githubusercontent.com/assets/326857/4018640/745de06e-2a51-11e4-917e-ca245ceabf68.png)

https://issues.jenkins-ci.org/browse/JENKINS-22820
I changed to 1.534 since 1.576 does not seem to have a POM?