gtkdoc-rebase: Fix log messages

Before:

Scanning documentation directory %s /usr/share/gtk-doc/html/dbus-glib
Reading index from dbus-glib.devhelp2
No On-line location for dbus-glib found
Local location of $package: /usr/share/gtk-doc/html/dbus-glib

After:

Scanning documentation directory /home/tingping/jhbuild/install/share/gtk-doc/html/harfbuzz
Reading index from harfbuzz.devhelp2
No On-line location for harfbuzz found
Local location of harfbuzz: /home/tingping/jhbuild/install/share/gtk-doc/html/harfbuzz