initSshPool() {
    if (!this.config.servers) throw new Error('Servers not filled')

    const servers = Array.isArray(this.config.servers)
      ? this.config.servers
      : [this.config.servers]

    const options = {
      ...this.options,
      key: this.config.key,
      asUser: this.config.asUser,
      strict: this.config.strict,
      verbosityLevel:
        this.config.verboseSSHLevel === undefined
          ? 0
          : this.config.verboseSSHLevel,
    }

    this.pool = new ConnectionPool(servers, options)

    this.emit('init:after_ssh_pool')
    return this
  }
Initialize SSH connections.

@returns {Shipit} for chaining