As prereq of support for S3 datasource, the hadoop-aws jar needs to be
in the Hadoop classpath. The jar is copied into the proper folder when
possible on the appropriate plugins, and otherwise can be provided from
a download URL by the user.
Additionally, set the correct value of DIB_HDFS_LIB_DIR on the Vanilla
plugin to avoid any unnecessary simlinking.
Partially-Implements: bp sahara-support-s3
Change-Id: I94c5b0055b87f6a4e1382118d0718e588fccfe87
a77a9a978a