Rustfmt: Switch 'indent_style' to 'Block'.

Temporarly switch to sidestep https://github.com/rust-lang-nursery/rustfmt/issues/2496
so people can start using rustfmt and the CI test succed.
4 jobs for <span class="ref-name">rustfmt</span> in 5 minutes and 9 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #10467
fedora:test

00:02:56

passed #10468
fedora:test_release

00:04:56

 
  Lint
manual #10470
allowed to fail manual
clippy
passed #10469
rustfmt

00:00:12