gaiad collect-gentxs resets all genesis parameters that are foreign to app_state

[alessio]

Forked from #3130

It appears that gaiad collect-gentxs unexpectedly modifies genesis.json parameters that do not belong to the Gaia's app state, represented in the genesis file's app_state JSON field.

Description

As A Gaia User
I Want to retain all values in genesis.json that do not belong to the app_state field unmodified.

Acceptance Criteria

Test case follows:

func TestGaiadCollectGentxs(t *testing.T) {
	t.Parallel()
	var customMaxBytes, customMaxGas int64 = 99999999, 1234567
	f := NewFixtures(t)

	// Initialise temporary directories
	gentxDir, err := ioutil.TempDir("", "")
	gentxDoc := filepath.Join(gentxDir, "gentx.json")
	require.NoError(t, err)

	// Reset testing path
	f.UnsafeResetAll()

	// Initialize keys
	f.KeysAdd(keyFoo)

	// Configure json output
	f.CLIConfig("output", "json")

	// Run init
	f.GDInit(keyFoo)

	// Customise genesis.json

	genFile := f.GenesisFile()
	genDoc, err := tmtypes.GenesisDocFromFile(genFile)
	require.NoError(t, err)
	genDoc.ConsensusParams.Block.MaxBytes = customMaxBytes
	genDoc.ConsensusParams.Block.MaxGas = customMaxGas
	genDoc.SaveAs(genFile)

	// Add account to genesis.json
	f.AddGenesisAccount(f.KeyAddress(keyFoo), startCoins)

	// Write gentx file
	f.GenTx(keyFoo, fmt.Sprintf("--output-document=%s", gentxDoc))

	// Collect gentxs from a custom directory
	f.CollectGenTxs(fmt.Sprintf("--gentx-dir=%s", gentxDir))

	genDoc, err = tmtypes.GenesisDocFromFile(genFile)
	require.NoError(t, err)
	require.Equal(t, genDoc.ConsensusParams.Block.MaxBytes, customMaxBytes)
	require.Equal(t, genDoc.ConsensusParams.Block.MaxGas, customMaxGas)

	f.Cleanup(gentxDir)
}

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[alessio]

CC @jaekwon @zmanian