RFR: 8272783: Epsilon: Refactor tests to improve performance

[Aleksey Shipilev]

Epsilon tests run in tier1, and they take considerable time, especially on low-core machines. We can refactor and simplify some of the tests for better performance.

The improvements are:
  - Dropping test heap sizes to 64M..256M, which saves time zeroing/zapping the heap area;
  - Dropping some configurations, notably out-of-box `-Xbatch -Xcomp` (which makes little sense, as C1/C2 paths would be taken by other configs)

Additionally, run configurations were reformatted to avoid long lines.


$ make run-test TEST=gc/epsilon

# Before
real	1m28.297s
user	9m2.689s
sys	0m18.370s

# After
real	1m0.396s
user	6m27.221s
sys	0m13.499s

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

Commit messages:
 - 8272783: Epsilon: Refactor tests to improve performance

Changes: https://git.openjdk.java.net/jdk/pull/5202/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5202&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272783
  Stats: 408 lines in 21 files changed: 271 ins; 29 del; 108 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5202.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5202/head:pull/5202

PR: https://git.openjdk.java.net/jdk/pull/5202