Tests for user account registration with phone number as the identifier

[exavolt]

Cases (all cases with clean database):

• register with a valid phone number -> OK
• register with phone number A, register with phone number A -> OK (same ID)
• register with phone number A, register with phone number B -> OK
• register with phone number A, confirm phone number A -> OK
• register with phone number A, confirm phone number A, register with phone number B -> OK
• register with phone number A, confirm phone number A, register with phone number A -> Fail
• register with phone number A, register with phone number B, confirm phone number A -> OK