remove UNIQUE constraint on tg_user.email_address

Bug: 1095010
Change-Id: I89f2a1b71e4bb04b0a0edf200277f7f545076f77
validate that lab controller FQDN is unique

Bug: 998374
Change-Id: I5c56bb0d52619eda4ab7ffcf261e27c8437616fa
add UNIQUE constraint for lab_controller.user_id

This is to prevent multiple lab controllers from sharing a single user
account, which does not work.

Bug: 1064710
Change-Id: Icc3b6599d761c536aae6b94a1cb8f58f01796994