Bump slf4j to 1.7.7

Currently in the odl we are using slf4j version 1.7.2

With this version we are hitting into the slf4j http://bugzilla.slf4j.org/show_bug.cgi?id=106 ( Obtaining a logger before Loggerfactory is assigned ).

Because of this some modules logs (very few ) will be missing ( this purely depends on the timing of the modules resolution in osgi environment).

This issue is resolved in the latest version 1.7.6

Thanks,
Anant.