returns memcached_up = 0 when fail to parse a stats values.

[f110]

fix #38

If there's an error when parse a stats value, returns memcached_up = 0.
because other metrics which succeeded in parsing value are useful.

If the LRU crawler does not run, ignoring some keys of related to it.

[grobie]

Thanks a lot for your contribution! I think we should not break the exporter for older memcached versions, so we'll need to find a solution how to handle the situation where a metric doesn't exist at all. See my comment below.

[f110]

Thank you for your review.

I fixed a compatible and some problems.
Could you please review again?

[f110]

@grobie ping

[f110]

@grobie Is there anything else to need for merging?

[grobie]

Thanks for the updates @f110! What do you think about logging key issues only on debug level, to not pollute the logs for old memcached versions?

[f110]

@grobie Thank you for review!

You are right!
This log is very noisy for older memcached. for example memcached 1.4.17 doesn't have the stats which relevant to lru_crawler ( lru_crawler_starts, crawler_items_checked etc...)

And, There is already to output very noisy log by the previous my PR (#46). So i decided to fix that problem too on this PR.

[grobie]

Thanks a lot for your contribution @f110. I squashed your commits together for readability and will release a new version shortly.

[f110]

Thank you for the merge.
And I appreciate your patience for my English.

[grobie]

Version v0.6.0 has been published https://groups.google.com/forum/#!topic/prometheus-announce/INfriYx3o1g

Thanks again @f110 and don't worry at all, your comments were easy to read and understand.