Brave Payments import failing can cause entire import to fail

[bsclifton]

Test plan

1. Have a Muon install which has a wallet with a non-zero balance
2. Launch Brave Core from the CLI with fresh profile
3. Use importer to import Brave (old). This should succeed (shows finish message)
4. Run import again, this time only picking Brave Payments
5. Because your wallet has a non-zero balance, the restore should fail
6. Error is logged to terminal
7. Import shows finish message, despite the second import failing

Description

When the upgrade happens from Muon to Brave Core, the importer is ran. If the importer encounters problems while importing Brave Payments, it cancels the import. This happens in the following scenarios:

• unable to get an instance of rewards service
• if wallet creation (creating the wallet to be imported into) fails
• restore fails
• backup of existing wallet fails (user already has a wallet, but with 0 balance)
• getting wallet properties (ex: balance) returns an error

Instead of cancelling the import (which may roll back the bookmarks import or other imported items), we should continue with the import. The user can then restore their wallet manually by either:

• trying to import Brave Payments only using Settings => Import (in Brave Core)
• Launching Muon, exporting keywords, restoring keywords in Brave Core

[LaurenWags]

Verified passed with

Brave	0.58.14 Chromium: 71.0.3578.98 (Official Build) (64-bit)
Revision	15234034d19b85dcd9a03b164ae89d04145d8368-refs/branch-heads/3578@{#897}
OS	Mac OS X

• Verified Test Plan in description
  This error was logged in terminal [27863:775:1218/124309.314326:ERROR:brave_profile_writer.cc(221)] Brave Rewards wallet existed before import and has a balance of 65.3453; skipping Brave Payments import.
  And the completion message still displayed
  

Verification passed on

Brave	0.58.14 Chromium: 71.0.3578.98 (Official Build) (64-bit)
Revision	15234034d19b85dcd9a03b164ae89d04145d8368-refs/branch-heads/3578@{#897}
OS	Windows 7

Used STR from OP, got log message
[12884:16068:1219/011131.137:ERROR:brave_profile_writer.cc(221)] Brave Rewards wallet existed before import and has a balance of 24; skipping Brave Payments import.

Also used a different wallets in b-c (27 BAT) and b-l (24BAT) and got this log message:
[12884:16068:1219/011315.591:ERROR:brave_profile_writer.cc(221)] Brave Rewards wallet existed before import and has a balance of 27; skipping Brave Payments import.

Verification passed on

Brave	0.58.15 Chromium: 71.0.3578.98 (Official Build) (64-bit)
Revision	15234034d19b85dcd9a03b164ae89d04145d8368-refs/branch-heads/3578@{#897}
OS	Linux

Used STR from OP, got log message
[28280:28280:1220/015034.784410:ERROR:brave_profile_writer.cc(221)] Brave Rewards wallet existed before import and has a balance of 22; skipping Brave Payments import.