RFR: 8260421: Shenandoah: Fix conc_mark_roots timing name and indentations

[Roman Kennke]

On Tue, 26 Jan 2021 16:55:02 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> Please review this trivial patch that renames conc_mark_roots timing name and fixes indentations
> 
> Test:
> - [x] hotspot_gc_shenandoah

Ok! Thanks!

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Marked as reviewed by rkennke (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2241