Avoid comparing domains when looking for an exact match of a local account

[happycoloredbanana]

This is supposed to fix #3064.

When looking for an exact account match, if the search string is in a user@domain form, check whether the domain is local before searching the accounts table.

[Gargron]

This is supposed to fix #3064.

Does it work?

[happycoloredbanana]

Yes. This is how I tested it:

Created a one-letter local account "i" and many remote accounts with the same letter in display_name. Tried /api/v1/accounts/search?q=i@mastodon.dev&limit=3 with curl and saw that only remote accounts are returned, although there's an exact match for the local account.
After the fix, it returns the exact match first and than - remote accounts.

[Gargron]

Perhaps that could be a unit test with those exact actions?

[happycoloredbanana]

Added a test.
Cannot figure out how Travis failures are even related.