RFR: JDK-8061729 : Update java/net tests to eliminate dependency on sun.net.www.MessageHeader and some other internal APIs [v6]

[Mahendra Chhipa]

> There are some regression tests depending on sun.net.www.MessageHeader, the internal API dependency should be removed. Some of other internal API dependancies are removed in following issues :
> JDK-8273142
> JDK-8268464
> JDK-8268133

Mahendra Chhipa has updated the pull request incrementally with one additional commit since the last revision:

  Implemented review comments :
  1. Use of Locale.ROOT
  2. Rewritten get(InputStream is) method as per comments.
  3. Corrected java doc comments.
  4. Removed use of is.available() method.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5937/files
  - new: https://git.openjdk.java.net/jdk/pull/5937/files/70a37be9..6820c0cd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5937&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5937&range=04-05

  Stats: 112 lines in 1 file changed: 19 ins; 15 del; 78 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5937.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5937/head:pull/5937

PR: https://git.openjdk.java.net/jdk/pull/5937