PROTON-2131: Improve and rationalise logger settings from the environment - Introduced a new environment variable PN_LOG which can be used to set   multiple logger levels active.
PROTON-2131: Improve and rationalise logger settings from the environment
- Introduced a new environment variable PN_LOG which can be used to set
  multiple logger levels active.

ChugR/qpid-proton,ssorj/qpid-proton,ssorj/qpid-proton,ChugR/qpid-proton,apache/qpid-proton,gemmellr/qpid-proton,ChugR/qpid-proton,gemmellr/qpid-proton,apache/qpid-proton,astitcher/qpid-proton,gemmellr/qpid-proton,astitcher/qpid-proton,kgiusti/qpid-proton,ssorj/qpid-proton,ssorj/qpid-proton,astitcher/qpid-proton,apache/qpid-proton,kgiusti/qpid-proton,astitcher/qpid-proton,ssorj/qpid-proton,apache/qpid-proton,ChugR/qpid-proton,kgiusti/qpid-proton,kgiusti/qpid-proton,astitcher/qpid-proton,kgiusti/qpid-proton,gemmellr/qpid-proton,ssorj/qpid-proton,ChugR/qpid-proton,kgiusti/qpid-proton,apache/qpid-proton,gemmellr/qpid-proton,astitcher/qpid-proton,ChugR/qpid-proton,gemmellr/qpid-proton,apache/qpid-proton