add statecouchdb to serial package list

when tests are run in parallel, CouchDB related test may not
get adequate time to successfully test asynchronous operations.

Signed-off-by: senthil <cendhu@gmail.com>

scripts/run-unit-tests.sh

@@ -16,6 +16,7 @@ excluded_packages=(
 # packages that must be run serially
 serial_packages=(
     "github.com/hyperledger/fabric/gossip/..."
+    "github.com/hyperledger/fabric/core/ledger/kvledger/txmgmt/statedb/statecouchdb"
 )
 
 # packages which need to be tested with build tag pkcs11