gradle: Pass bnd gradle plugin classpath to build.gradle

Plugin coordinates are in gradle.properties and ivy repository is setup
in settings.gradle. We do that to use the plugin from the cloudbees
build.

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
gradle template: Update to use bnd gradle plugin from jcenter

The version of the bnd gradle plugin is based upon the version of bndlib
used in the build.

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
Merge pull request #938 from bjhargrave/gradle-repo-plugin

gradle: Pass bnd gradle plugin classpath to build.gradle