RFR: 8205438: Re-enable shebang tests in test/jdk/tools/launchers/SourceMode.java

[Jonathan Gibbons]

Please review a test fix to re-enable shebang tests in 
test/jdk/tools/launchers/SourceMode.java .

The test cases for invoking the source launcher via the shebang 
mechanism have been disabled because they were adversely affected by the 
very long pathnames on our internal test infastructure, causing the test 
cases to overflow the system limit of 128 characters for the first line 
of a shebang file

The fix is to run jlink to create a small image that can be addressed by 
a short relative path.

Some of the test cases on macOS and Solaris remain explicitly disabled 
because of the inconsistencies in the system-level support for shebang 
execution.

Finally, the use of hard-coded version numbers in the test is changed to 
avoid having to add this test to the list of tests that need to be 
modified at the beginning of each release.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8205438
Webrev: http://cr.openjdk.java.net/~jjg/8205438/webrev.00/