Fix net::ERR_INSUFFICIENT_RESOURCES errors on HTTP2 introduced in 5.4.1

[jvigliotta]

addresses: #373

Main fix here is the removal of keapalive = true for fetch options. This was introduced to increase load times and testing seemed to indicate it did, though now it's believed that was a false positive. This flag will crush Open MCT using the MCWS Adapter plugin on large quantities of requests. The fix is to remove. We'll do testing to ensure load times aren't affected. Additional fixes for race conditions introduced in trying to fix the underlying issue are included as well as they are good changes.

[davetsay]

Suggested change

	async getPersistenceNamespaces() {
	async getPersistenceNamespaces() {
	if (!this.persistenceNamespaces) {
	this.persistenceNamespaces = (async () => {
	const rootNamespaces = await this.getRootNamespaces();
	const allContainedNamespaces = await this.getAllContainedNamespaces(rootNamespaces);
	const persistenceNamespaces = [...rootNamespaces, ...allContainedNamespaces];
	return persistenceNamespaces;
	})();
	}
	return this.persistenceNamespaces;
	}