Fix: lookup more specific DNS names directly

[simonrw]

Motivation

When resolving DNS names, if someone adds a more specific entry to an existing entry with a wildcard, the more specific name is not matched. For example:

ADD foo.example.com 1.2.3.4
ADD *.example.com 5.6.7.8

dig foo.example.com => 5.6.7.8
dig bar.example.com => 5.6.7.8

A request to foo.example.com should resolve to 1.2.3.4

Changes

Look up the DNS name by string, which is what we store in the add_host method

[coveralls]

coverage: 84.28% (+0.02%) from 84.263%
when pulling 6697b3d on fix/dns-hostname-overrides-matching
into 0595d87 on master.

[github-actions]

LocalStack Community integration with Pro

       2 files         2 suites   1h 11m 31s ⏱️
2 397 tests 2 169 ✔️ 228 💤 0 ❌
2 398 runs  2 169 ✔️ 229 💤 0 ❌

Results for commit 6697b3d.

[dfangl]

Good catch! The trailing dot inconsistency were quite annoying!