Add python-shell to RDEPENDS for network.bb

netman.py has a runtime dependency on glob which is provided by
the python-shell package.  Adding a direct run-time dependency
to the recipe is useful.

Change-Id: I212532a2987e6bde44f56e7e0f632c7e9e5c7b67
Signed-off-by: Patrick Venture <venture@google.com>