teuthology: add an extra_packages flag to install

Some tests require additional packages
(e.g., java bindings, hadoop bindings).
Extend the install task to allow for those
packages to be specified in the yaml files.

Signed-off-by: Joe Buck <jbbuck@gmail.com>
Reviewed-by: Sam Lang <sam.lang@inktank.com>
teuthology: remove CEPH_JAVA_PATH

Since teuthology now uses debian packages,
we do not need to set this in workunit.
The one test that uses this now tests for
it locally.

Signed-off-by: Joe Buck <jbbuck@gmail.com>