consensus/params: set default values for BIP9Deployment

While chainparams should explicilty set values for each possible
entry in vDeployments, in the past that has been missed resulting
in potential undefined behaviour due to accessing unitinitialized
data. Reduce the severity of future bugs of that nature by providing
benign default values. Adds a unit test to alert if the default value
is not overwritten for the real chains (NEVER_ACTIVE/NEVER_ACTIVE rather
than NEVER_ACTIVE/NO_TIMEOUT).

src/test/versionbits_tests.cpp

@@ -275,6 +275,7 @@ static void check_computeblockversion(const Consensus::Params& params, Consensus
         nStartTime == Consensus::BIP9Deployment::NEVER_ACTIVE)
     {
         BOOST_CHECK_EQUAL(min_activation_height, 0);
+        BOOST_CHECK_EQUAL(nTimeout, Consensus::BIP9Deployment::NO_TIMEOUT);
         return;
     }