[list] Automatic generated id

[AndreKoepke]

Describe the bug
The mdc-list and the underlaying mdc-list-items getting automatic a id. Even when the id is manually provided.
The id is in this schema <componet-name>-<n> - so if we have a two lists like this ...

list1 (#mdc-list-1)
 |--> item1 (#mdc-list-item-1)
 |--> item2 (#mdc-list-item-2)
list2 (#mdc-list-2)
 |--> item1 (#mdc-list-item-3)
 |--> item2  (#mdc-list-item-4)

Then the id's a automatic set somewhere. It doesn't matter if we set a id manually (with one variant of <mdc-list-item id="test" [id]="'test'" [attr.id]="'test'" ...), there is always the generated id.

To Reproduce
Steps to reproduce the behavior:

1. Setup a list and inspect the id's.

Expected behavior
If a id was set manually, then it never gets overwritten.
Otherwise it is really hard to write test-cases for e2e in a big project, when the id`s "randomly" changed.

Screenshots
It seems, that the behaviour is also on the examples.

What Angular MDC version are you using? 5.1.1

What OS are you using?: Linux and Windows

What browser(s) is this bug affecting?: Chrome and Firefox