Relocates generate_random_password to common.utils

Reasons:
- instance.models._create_resources is still uses uuid as root_password.
- generate_random_password needs to be used in a diferent module, so it
  is a candidate to be moved to trove.common.utils, so that any
  new change could be made at one place only, affecting all used-cases.

Changes:
- Relocates generate_random_password to common.utils
- Replaces uuidutils.generate_uuid with generate_random_password in
  trove.instance.models._create_resources(password_length).

Change-Id: Ib58bf83b3c052261418907db41ca963768d2e710
Closes-Bug: #1264330
Updates oslo.context

This change is needed for uuidutils removal in Trove

13eb01c Adding domain to context and log
12bcdb7 Remove vim header
bdabd51 Remove uuidutils imports in oslo modules

Change-Id: I3b4eead93fc2d12ccb6a0837f9100b784b25d8dd
Replace oslo.uuidutils module with trove.utils

Oslo is removing uuidutils during the icehouse cycle.
Consequently we need to remove all references to uuidutils, and
replace them with the corresponding function from trove.utils.

Change-Id: Idd4b25e98624dfb6a25e275cac44a54324f50449
Closes-bug: 1253497