RFR: Loom test groups for development/porting use [v3]

[Aleksey Shipilev]

> Porting/development work would be much simpler if we had a comprehensive test group with Loom-specific tests. There is `tier1_loom`, but it probably has a separate meaning. We can add some test groups with Loom-specific tests. I basically went and added tests that are added/substantially-modified by Loom, judging by a [recent webrev](https://builds.shipilev.net/patch-openjdk-loom-fibers/).
> 
> Sample run:
> 
> 
> $ time CONF=linux-x86_64-server-fastdebug make test TEST="hotspot_loom jdk_loom"
> ...
> ==============================
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR   
>    jtreg:test/hotspot/jtreg:hotspot_loom                63    63     0     0   
>    jtreg:test/jdk:jdk_loom                             187   187     0     0   
> ==============================
> TEST SUCCESS
> 
> Finished building target 'test' in configuration 'linux-x86_64-server-fastdebug'
> 
> real	6m37.938s
> user	54m13.043s
> sys	2m12.437s

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  More reviews

-------------

Changes:
  - all: https://git.openjdk.java.net/loom/pull/74/files
  - new: https://git.openjdk.java.net/loom/pull/74/files/b3ed47dc..4764f62d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=74&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=74&range=01-02

  Stats: 10 lines in 2 files changed: 2 ins; 4 del; 4 mod
  Patch: https://git.openjdk.java.net/loom/pull/74.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/74/head:pull/74

PR: https://git.openjdk.java.net/loom/pull/74