message: Prevent duplicate server creation in GCP
  This change disables the "create server" button in GCP when server
  creation is in progress.
diff: @@ -231,13 +231,16 @@ export class GcpCreateServerApp extends LitElement {
  <span slot="step-title">Create your Google Cloud Platform project.</span>
  <span slot="step-description">This will create a new project on your GCP account to hold your Outline servers.</span>
  <span slot="step-action">
  - <paper-button
  + ${this.isProjectBeingCreated ?
  + // TODO: Support canceling server creation.
  + html`<paper-button disabled="true">IN PROGRESS...</paper-button>` :
  + html`<paper-button
  id="createServerButton"
  @tap="${this.handleProjectSetupNextTap}"
  ?disabled="${
  !this.isProjectSetupNextEnabled(this.selectedProjectId, this.selectedBillingAccountId)}">
  CREATE PROJECT
  - </paper-button>
  + </paper-button>`}
  </span>
  <div class="section">
  <div class="section-header">
  