MB-10496: Add jemalloc as a cbdeps dependancy for Debian 7

Change-Id: I1599a7f1e591d37aed079401dd02bad145488b44
Reviewed-on: http://review.couchbase.org/43849
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>