test: Disable several (sub)tests with cli

Reason for each test:
wallet_labels.py: uses createmultiwallet, which is currently not
compatible with cli
rpc_whitelist.py: Relies on direct RPC calls
wallet_encryption.py: Null characters cannot be passed to
suprocess.Popen, which is used to send the commands to
bitcoin-cli.

test/functional/rpc_whitelist.py

@@ -33,6 +33,7 @@ class RPCWhitelistTest(BitcoinTestFramework):
 
     def set_test_params(self):
         self.num_nodes = 1
+        self.supports_cli = False
 
     def run_test(self):
         # 0 => Username

test/functional/wallet_encryption.py

@@ -90,6 +90,7 @@ class WalletEncryptionTest(BitcoinTestFramework):
         assert_equal(actual_time, expected_time)
         self.nodes[0].walletlock()
 
+        if not self.options.usecli: # can't be done with the test framework for cli since subprocess.Popen doesn't allow null characters
             # Test passphrase with null characters
             passphrase_with_nulls = "Phrase\0With\0Nulls"
             self.nodes[0].walletpassphrasechange(passphrase2, passphrase_with_nulls)

test/functional/wallet_send.py

@@ -29,6 +29,7 @@ class WalletSendTest(BitcoinTestFramework):
         self.num_nodes = 2
         # whitelist peers to speed up tx relay / mempool sync
         self.noban_tx_relay = True
+        self.supports_cli = False
         self.extra_args = [
             ["-walletrbf=1"],
             ["-walletrbf=1"]