Updating gzip tests to include 1 other flavor
450855 - GZipFilter declaration order can result in MIGHT_COMPRESS

+ Adding testcase GzipFilterLayeredTest to demonstrate this bug
+ Some cleanup of Gzip testing behavior to be easier to follow
  (less reliance on GzipTester utility class)
Some cleanup of the Gzip tests

+ Seeing more edge cases that can cause problems.
  Set those to @Ignore for greg to take a look at
test names with ':' makes ms windows very unhappy
replace GzipTester.issueRequest with preexisting GzipTester.executeRequest
Merge branch 'jetty-9.2.x'

Conflicts:
	jetty-servlets/src/test/java/org/eclipse/jetty/server/handler/gzip/GzipContentLengthTest.java
	jetty-servlets/src/test/java/org/eclipse/jetty/server/handler/gzip/GzipTester.java
	jetty-servlets/src/test/resources/jetty-logging.properties