Add new elasticsearch metrics since 0.18+.
Add new elasticsearch metrics since 0.18+.

Also refactored the fetch method to greatly simplify the
addition of new metrics - no longer uses the old Perl switch
module, rather uses pmda_pmid_name() interface to lookup the
individual metric/instance values in global fetch hash.

adfernandes/pcp,ryandoyle/pcp_original,edwardt/pcp,wuliming/pcp,tjanez/pcp,ryandoyle/pcp_original,mbaldessari/pcp,aeg-aeg/pcpfans,mbaldessari/pcp,mbaldessari/pcp,edwardt/pcp,wuliming/pcp,adfernandes/pcp,prasincs/pcp,prasincs/pcp,prasincs/pcp,ryandoyle/pcp_original,edwardt/pcp,prasincs/pcp,adfernandes/pcp,tjanez/pcp,prasincs/pcp,aeg-aeg/pcpfans,edwardt/pcp,wuliming/pcp,tjanez/pcp,prasincs/pcp,wuliming/pcp,tjanez/pcp,wuliming/pcp,wuliming/pcp,ryandoyle/pcp_original,mbaldessari/pcp,andyvand/cygpcpfans,ryandoyle/pcp_original,prasincs/pcp,tjanez/pcp,adfernandes/pcp,andyvand/cygpcpfans,prasincs/pcp,aeg-aeg/pcpfans,mbaldessari/pcp,aeg-aeg/pcpfans,edwardt/pcp,ryandoyle/pcp_original,mbaldessari/pcp,edwardt/pcp,andyvand/cygpcpfans,edwardt/pcp,adfernandes/pcp,andyvand/cygpcpfans,ryandoyle/pcp_original,aeg-aeg/pcpfans,wuliming/pcp,tjanez/pcp,ryandoyle/pcp_original,tjanez/pcp,wuliming/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,andyvand/cygpcpfans,aeg-aeg/pcpfans,adfernandes/pcp,adfernandes/pcp,edwardt/pcp,andyvand/cygpcpfans,adfernandes/pcp,tjanez/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans