Disable TestRestartAfterCheckpoint Test

The TestRestartAfterCheckpoint test exhibits intermittent failures which
is causing problems in CI and erroneously flagging builds as failed
which should otherwise pass.  This changeset disables that test until a
more permanent solution can be found.

This is related to, (though does not resolve) JIRA issue:

https://jira.hyperledger.org/browse/FAB-624

Change-Id: Ic583758130218104f78b6b5bcc439dcfbc6339df
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>

consensus/simplebft/simplebft_test.go

@@ -503,6 +503,8 @@ func TestRestartAfterCommit(t *testing.T) {
 }
 
 func TestRestartAfterCheckpoint(t *testing.T) {
+	// TODO re-enable this test after https://jira.hyperledger.org/browse/FAB-624 has been resolved
+	t.Skip()
 	N := uint64(4)
 	sys := newTestSystem(N)
 	var repls []*SBFT