allow slurmdbd_storage_port to be an empty string (support socket connection to DB)

[jakerundall]

Allow slurmdbd_storage_port to be an empty string ("" or ''), which supports slurmdbd connecting to the DB via a socket rather than via TCP/IP.

Adjust the template for slurmdbd.conf so that if any value is an empty string (''), then put "" in as the value.

See #57 .

[treydock]

A unit test for the new behavior would be ideal, similar to this:

puppet-slurm/spec/shared_examples/slurm_slurmdbd_config.rb

Lines 69 to 75 in 1b1efc8

	context 'when slurmdbd_storage_pass => "foobar"' do
	let(:param_override) { { slurmdbd_storage_pass: 'foobar' } }
	it 'overrides values' do
	verify_contents(catalogue, 'slurmdbd.conf', ['StoragePass=foobar'])
	end
	end

[treydock]

Might also need to rebase after some recent updates

[jakerundall]

OK, ready for another look, thanks! Sorry for the delay.

[treydock]

This is being released with v4.0.1 once Github Actions complete