CtsMultiUserHostTestCases improvements:

- Removed unused imports.
- Replaced JUnit assertions by Truth.
- Added checkstyle hook.
- Replaced getDevice() by mDevice.
- Removed splitUserSystem support.
- Removed redundant logs to commands and outputs (they're already
  loged by ITestDevice)
- Created SupportMultiUsersRule
- Spun SetUsersRestrictionsTest from CreateUsersPermissionTest so the
  latter can use SupportMultiUsersRule.
- Changed how test cases are automatically removed.
- Removed dead code.
- Used String pattern formatting on CLog calls.

Test: atest CtsMultiUserHostTestCases # on flame_car and aosp_coral

Bug: 168919650
Bug: 165406498
Bug: 137101239

Change-Id: Ieeeef55f8fbf3d04a137a2d1047af85b53ea215f
7 files changed