Fix python-requests package dependencies.

python-ceph does not require requests, but ceph-common does (for ceph-brag).

Signed-off-by: Dan Mick <dan.mick@inktank.com>
Merge pull request #1323 from ceph/wip-requests-dependencies

Fix python-requests package dependencies.

Backport: firefly
Reviewed-by: Sage Weil <sage@inktank.com>