Redis: Adds support for checking length of sets, sorted sets and hashes as well.

Also, send 0 as the value in case the type is unsupported or doesn't exist.
SNMP checks| First pass at supporting table querying
SNMP checks| Extract table tags in a function + cleanup
SNMP Checks| Use correct name
SNMP Checks| Reallow the possibility for non mib loaded oid
SNMP Checks| Fix tests and bug for oid querying
SNMP Checks| prettyPrint the tags and remove debug statement
SNMP Checks| remove accidental commit of dev test configuration
SNMP Checks| Don't query for no oids
SNMP Checks| Add test case for querying table
SNMP checks| Documentation
SNMP Checks| Better logging to troubleshoot issues

Also remove an unused variable
SNMP Checks| Make the tests more robust
SNMP Checks| Don't use assertGreater for 2.6 compatibility
SNMP checks| Fix small mistake in the test code
Merge branch 'master' into rudy/snmp-table
SNMP checks| Fix the yaml example
Merge branch 'master' into rudy/snmp-table
SNMP checks| Fix bug where we overwrote all our results
SNMP checks| Don't completely fail the checks for only one metric