Wrap verbose logging in separate subroutine

We have to check if the verbose flag is set every time we want to log
something to the console. Wrap this in a separate subroutine that does
the checking and only call that subroutine directly.

This means that the logging functionality in Repository has to be
changed to return a string rather than handling the logging since that
class can't check if verbose is set.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>