Well, all the easy ones, anyway.

For some reason `// ignore:` isn't working for me so I've disabled
lints that need that. Also disabled those that require a ton of work
(which I'm doing, but not in this PR, to keep it reviewable).

This adds:
- avoid_init_to_null
- library_names
- package_api_docs
- package_names
- package_prefixed_library_names
- prefer_is_not_empty
- sort_constructors_first
- sort_unnamed_constructors_first
- unnecessary_getters_setters

flutter start's method of finding devices to run the app on is not suitable for flutter drive.

This commit also refactors several tool services to allow mocking in unit tests.

remove the device factory methods as well as the device cache

rename to printTrace(), printStatus(), and printError()

remove device type specific checks

Sometimes "adb devices" prints a header. We should skip over the header
instead of complaining that we don't recognize it.

Fixes #1293

Catch the error and log a warning.

Fixes #1050

This is yet another hack on top of adb log handling.
This is fragile, but w/o this if you device time is out
of sync, you can't trace.

@abarth

update the min api level in the generated android manifest; use constants for the android version name