RFR: 8287352: DockerTestUtils::execute shows incorrect elapsed time [v2]

[Ioi Lam]

> Please review this small change to improve the test reporting:
> 
> - Calculating elapsed time after child process has exited
> - Do not print `"Child process STDOUT is trimmed ..."` unless the lines are really trimmed.

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  Renamed trimLines() -> limitLines()

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8897/files
  - new: https://git.openjdk.java.net/jdk/pull/8897/files/6a225656..d1cb5946

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8897&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8897&range=00-01

  Stats: 6 lines in 1 file changed: 0 ins; 1 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8897.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8897/head:pull/8897

PR: https://git.openjdk.java.net/jdk/pull/8897