reset counter type to it's initial value

It was a COUNTER, not a GAUGE before it got accidentally deleted by
6372ca6a38.
zookeeper: add mention in README & AUTHORS
RPM specfile: add zookeeper plugin
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)
Merge pull request #834 from mfournier/zookeeper_build_error

zookeeper: initialize a variable
Resolved issue of MQTT subscribe thread not running when fork to background.
Merge remote-tracking branch 'upstream/master'