Refactor tests to async/await (#72)

Remove a bunch of `expectAsync` since the work is all tracked in the
`Future` the test runner will already fail if something doesn't
complete.

In virtual_host test extract common server handling to a `setUp` and
`tearDown`. Remove the test 'multiple-host' since it is identical to
'wildcard-sub-domain' test.

Tweak travis config to only run the analyzer with the dev SDK to
work around false errors on older SDKs.

Rename some test utilities from `test` to `check` to avoid conflicts
with the `test` function from `package:test`.

Author: natebosch

.travis.yml

@@ -6,12 +6,14 @@ dart:
 
 dart_task:
   - test
-  - dartanalyzer: --fatal-infos --fatal-warnings .
 
 matrix:
   include:
-  - dart: dev
-    dart_task: dartfmt
+    - dart: dev
+      dart_task: dartfmt
+    - dart: dev
+      dart_task:
+        dartanalyzer: --fatal-infos --fatal-warnings .
 
 # Only building master means that we don't run two builds for each pull request.
 branches: