lvmconfig: display comment about value from existing config being used

lvmconfig: display comment about value from existing config being used

Display comment abour value from existing config being used. For example:

$ lvmconfig --type full --withsummary report/compact_output report/buffered

 # Configuration option report/compact_output.
 # Do not print empty report fields.
 # Value defined in existing configuration has been used for this setting.
 compact_output=1

 # Configuration option report/buffered.
 # Buffer report output.
 buffered=1