Office 365 - Give permission to a someone for all calendars

Following powershell will list mailbox with resource type as "Room" and then it will add user@domain.com as Editor for that rooms calendar.

$rooms = get-mailbox | where {$_.resourcetype -eq "room"}
foreach ($room in $rooms)
{
Add-MailboxFolderPermission -Identity ($room.windowsliveid + ":\calendar") -user user@domain.com -AccessRights Editor
}