Fix Nolabels parse metrics

[adityacs]

What this PR does / why we need it:
Fixes tailing with no labels
Which issue(s) this PR fixes:
Fixes #765

[adityacs]

@sandlis Kindly review this

[sandeepsukhani]

@adityacs I just saw your PR while I was going to open one with my fix.
Please check out how I fixed it which I feel would be good to go with instead of checking no labels flag at 2 places and recreating labels instance for each logline. sandeepsukhani@1d1c327

I do not mind if you want to copy all of the changes from my branch and improve it further since you got to open the PR first.
Thanks for the PR!

[adityacs]

@sandlis Thanks for considering my code change. However, your code is elegant. Kindly close this PR and push your changes.

Sorry for hijacking your task 😄

[sandeepsukhani]

@adityacs It is not a problem. Since you started working on it first, I would encourage you to go ahead with this instead. We appreciate and encourage more people to contribute to Loki.
Please let me know if you need any help with this from my side.

[adityacs]

@sandlis Very encouraging attitude. Thanks a lot 😄

[adityacs]

@sandlis I have copied the code from your branch and pushed the changes. Kindly review

[sandeepsukhani]

LGTM