Fix for test/jdk/tools/launcher ExecutionEnvironment.java and Test7029048.java tests on Alpine Linux

[Alexander Scherbatiy]

Hello,


Two jdk/tools/launcher tests fail because they expect that the launcher 
does not pollute LD_LIBRARY_PATH.

This is not the case for Alpine Linux (more details are in the comment 
for RequiresSetenv() method from java_md_solinux.c [1]).

The proposed fix adds isMusl and isExpandedSharedLibraryPath flags to 
the TestHelper class to be able to check that LD_LIBRARY_PATH is 
modified because of the system requirements:

http://cr.openjdk.java.net/~alexsch/portola/tests/launcher/webrev.00

The code for isMuslLibc() is copied from VMProps.java jtreg extension 
which leads to the code duplication. May be it would be better to reuse 
the same method in both classes.

[1] 
https://github.com/openjdk/portola/blob/93b8ad5f1ef3d2a260fa580db0113bb40db83a72/src/java.base/unix/native/libjli/java_md_solinux.c#L244


Thanks,

Alexander.