Add a plugin for monitoring zookeeper

This adds a simple plugin to read data from Zookeeper's MNTR
command to allow for easy monitoring of Zookeeper from collectd
without requiring jmx
Add information to collectd.conf (5) for the zookeeper plugin
Use generic types for a few more of the zookeeper metrics
Adjust for changes in old collectd so that I can regen auto*
regen auto*
zookeeper: initialize a variable

If the loop on line 132 doesn't iterate at least once, the function would
return the "sk" variable uninitialized.

This fixes the following build error:

cc1: warnings being treated as errors
zookeeper.c: In function 'zookeeper_read':
zookeeper.c:107: warning: 'sk' may be used uninitialized in this function
make[3]: *** [zookeeper.lo] Error 1

(caught by gcc version 4.1.2 on EL5)
reintroduce counter, killed by error
reset counter type to it's initial value

It was a COUNTER, not a GAUGE before it got accidentally deleted by
6372ca6a38.