Ensure that the directory for the gc.log file exists
Quote the $ES_HOME reference when searching for elasticsearch.in.sh
Use eval to better handle paths with spaces

The can ES_GC_LOG_FILE refer to a path with spaces, so must be quoted. But doing that
will not work properly when invoking java (one level of unexpected quotes appearing), so
we need to resolve them before that again.

This commit changes the way JAVA_OPTS and ES_CLASSPATH are used, and fixes up the quoting
for the es.path.home variable.
Include relevant defaults for ES_GC_LOG_FILE in the rpm/deb files