Add missed docs, use class vars for log conf/context/def.format

Both for syslog and local logging, user can specify custom
name for logging config erb template to be used as well as
custom logging context and default format headers

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>
Merge pull request #1 from bogdando/logging_fixes

Add missed docs, use class vars for log conf/context/def.format
Fix hardcoded

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>
Fix logic typo

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>
Merge pull request #2 from bogdando/logging_fixes

Fix hardcoded
rename cinder logging conf

Change-Id: Ia5d1078a0a247e95ce6ad092e5aa481a9c8bd241
Consider #1167329 fix for logdir option

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>