try to guess JAVA_HOME if absent from environment in the a hopefully por...

This is a fix for WFLY-1902

Remove useless $JAVA variable check and insert attempt to guess JAVA_HOME in case jconsole executable is in PATH.

Additionally I added quotes to call of jconsole to avoid parameter passing troubles when special characters are involved.

I've tested the script to work on fedora18, rhel5, aix6, hp-ux and solaris9.

On non-rpm platforms it is unlikely the change to have any effect because it is unlikely to have jconsole in PATH without JAVA_HOME. In such case error is printed to user as before. The readlink command is used in a portable way though so it may work if jconsole is present. Only aix seems to lack a readlink command but in such case error is also printed to user. jconsole.sh should also work on mac *no worse* than without the modification. But I can't test that.

On fedora and RHEL the change helps user to have jconsole.sh working with default java installation where executables from the JDK are present but JAVA_HOME is not set.