https://bugzilla.redhat.com/show_bug.cgi?id=895882

virDomainSnapshot.getDomain() and virDomainSnapshot.getConnect()
wrappers around virDomainSnapshotGet{Domain,Connect} were not supposed
to be ever implemented. The class should contain proper domain() and
connect() accessors that fetch python objects stored internally within
the class. While domain() was already provided, connect() was missing.

This patch adds connect() method to virDomainSnapshot class and
reimplements getDomain() and getConnect() methods as aliases to domain()
and connect() for backward compatibility.