Handle getcwd FileNotFoundError

[jiasli]

Fix Azure/azure-cli#12239

On Linux, if the working directory has been deleted (or created later), getcwd will raise FileNotFoundError.

This PR fixes this issue by showing a warning and continue.

To test, run

mkdir t1
cd t1
rmdir ~/t1
python ~/knack/examples/exapp2 abc list

Now it shows warning:

The working directory has been deleted or recreated. Local config is ignored.

In Azure CLI, the warning appears twice because besides the initiation of CLIConfig from Knack

knack/knack/cli.py

Lines 83 to 86 in 2036b78

	self.config = config_cls(
	config_dir=config_dir or os.path.expanduser(os.path.join('~', '.{}'.format(cli_name))),
	config_env_var_prefix=config_env_var_prefix or cli_name.upper()
	)

Azure CLI is also creating a CLIConfig instance.

https://github.com/Azure/azure-cli/blob/77fcc2b071bd448e858807946e4f2ef66db9ae4e/src/azure-cli-core/azure/cli/core/extension/__init__.py#L16

az_config = CLIConfig(config_dir=GLOBAL_CONFIG_DIR, config_env_var_prefix=ENV_VAR_PREFIX)

We may fix it in Azure CLI later.

[qianwens]