RFR: 8261752: Multiple GC test are missing memory requirements

[Christoph Göttschkes]

I used systemd to figure out which memory requirement makes sense for which test:

$ systemd-run --user --scope -p MemoryMax=768M -p MemorySwapMax=0 /usr/bin/make TEST="..." test

Tests succeeding with `768M` of MemoryMax got a requirement of 1G, all others got 2G and succeeded with a MemoryMax of 1536M.

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

Commit messages:
 - Adds memory requirements.

Changes: https://git.openjdk.java.net/jdk/pull/2575/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2575&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261752
  Stats: 7 lines in 7 files changed: 2 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2575.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2575/head:pull/2575

PR: https://git.openjdk.java.net/jdk/pull/2575