Fix java/nio/file/FileStore/Basic.java test by ignoring /run/user/* mount points

java/nio/file/FileStore/Basic.java test is failing on Linux with the following stacktrace:

/run/user/1000/doc (portal) (name=portal type=fuse.portal)
----------System.err:(16/985)----------
java.nio.file.FileSystemException: /run/user/1000/doc: Operation not permitted
at java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:100)
at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:106)
at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111)
at java.base/sun.nio.fs.UnixFileStore.readAttributes(UnixFileStore.java:115)
at java.base/sun.nio.fs.UnixFileStore.getTotalSpace(UnixFileStore.java:122)
at Basic.doTests(Basic.java:135)
at Basic.main(Basic.java:49)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:577)
at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:312)
at java.base/java.lang.Thread.run(Thread.java:833)

The problem is the same as in JDK-8272369 and caused by the mount points of fuse.portal type that return EPERM: Operation not permitted on access.

To reproduce the problem with /run/user/1000/doc mount on Fedora 34 one can run:

$ /usr/libexec/xdg-document-portal

This behaviour is also known to cause problems to various Linux utilities, references:

https://lists.debian.org/debian-user/2021/06/msg00022.html
https://bugzilla.redhat.com/show_bug.cgi?id=1952714
https://bugzilla.redhat.com/show_bug.cgi?id=1913358
https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=9a38d499ca16f2f4304992eb1ab0894cd0b478e1
https://github.com/flatpak/xdg-desktop-portal/issues/512