I used new-VMHostAccount -UserAccount "user" -password pass -AssignGroups "users", "esx_host_admin".
this command appear to create the user account as assign the user into the right group.
But, I can't figure out how the give "Grant shell access to this user" from powershell?
Try this:
Author of the upcoming book: Managing VMware Infrastructure with PowerShell
Co-Host, PowerScripting Podcast (http://powerscripting.net)
new-VMHostAccount -UserAccount "user" -password pass -AssignGroups "users", "esx_host_admin" -GrantShellAccess
For all the switches look in the vsphere 5.5. documentation center
then search for new-VMHostAccount