passenger_stats collector - rewrite
passenger_stats collector - rewrite

This is a slight rewrite of collector of passenger-stats.
Most notablechanges are:
  * ditch unnecessary subprocess() calls - use Python!
  * use compiled RE
  * clean up and re-write code - pretty much all of it
  * fix names of emitted metrics
  * collector no longer ends up as a Zombie process

Signed-off-by: Zdenek Styblik <dc4a2b801ed63d5bdee592442eca3911ae928322@icflix.com>

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