Create directories for docjar, srcjar and jar targets

The ant target 'mvn-install' doesn't create all directories needed,
therefore jenkins builder is failing to build artifacts

http://sdkbuilds.couchbase.com/job/java-snapshot-build/18/console

Change-Id: I8acb12eee4c1214febd2de8f49cdad3a8de706f2
Reviewed-on: http://review.couchbase.org/25077
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Deepti Dawar <deepti.dawar@globallogic.com>