log: log warnings and errors via report if set; add log_set_report* fns

log: log warnings and errors via report if set; add log_set_report* fns

This patch adds structures and functions to reroute error and warning
logs to log report, if it's set.

There are 5 new functions:
  - log_set_report
    Set log report where logging will be rerouted.

  - log_set_report_context
    Set context globally so any report_cmdlog call will use it.

  - log_set_report_object_type
    Set object type globally so any report_cmdlog call will use it.

  - log_set_report_object_name_and_id
    Set object ID and name globally so any report_cmdlog call will use it.

  - log_set_report_object_group_and_group_id
    Set object group ID and name globally so any report_cmdlog call will use it.

These functions will be called during LVM command processing so any logs
which are rerouted to log report contain proper information about current
processing state.