bnd-maven-plugin: create plugin descriptor in process-classes phase
bnd-maven-plugin: create plugin descriptor in process-classes phase

With older versions of maven (e.g. 3.1.1), the descriptor generation
occurred before the classes were compiled. This resulted in the mojo
not being processed into the descriptor.

Signed-off-by: BJ Hargrave <3d26bb3930946e3370762d769a073cece444c2d8@bjhargrave.com>

GEBIT/bnd,lostiniceland/bnd,lostiniceland/bnd,xtracoder/bnd,mcculls/bnd,lostiniceland/bnd,GEBIT/bnd,psoreide/bnd,psoreide/bnd,mcculls/bnd,magnet/bnd,xtracoder/bnd,joansmith/bnd,mcculls/bnd,joansmith/bnd,magnet/bnd,magnet/bnd,psoreide/bnd