Before attempting to load any modules make sure Jetpack is connected

A key conditional checking to see if Jetpack is connected before loading any module was
removed in fc16302fe65c561af685cc689cb68e36e6dc0480. This commit re-adds that check but
before Jetpack even attempts to load any modules at all.

Fixes #1047
Allowing module loading in dev mode. Thanks @lezama!
Merge pull request #1054 from Automattic/modules-disconnect

Before attempting to load any modules make sure Jetpack is connected