gnome-power-manager: fix configure

* configure looks for libgnome-keyring (there is no option --disable-keyring)
* to have a daemon put gnome-keyring to RRECOMMENDS.

Error message was:
| Package gnome-keyring-1 was not found in the pkg-config search path.
| Perhaps you should add the directory containing `gnome-keyring-1.pc'
| to the PKG_CONFIG_PATH environment variable
| No package 'gnome-keyring-1' found
| configure:13934: $? = 1
| configure:13952: result: no
| No package 'gnome-keyring-1' found
| configure:13978: error: Package requirements (

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>